In no particular order except for the broad categories, a list of places that sell stuff that is relevant to our interests. Personal experience of these, good or bad, would be useful on the discussion page.
London services & workshops
- Blueprint model shop They have a laser cutter, and may also do plastic board.
- Hamar acrylic (ask for Terry). "Hamar tend to turn things around in a couple of days. They can do all sorts of complex plastic fabbing as well as simple cutting. Excellent variety of materials in stock." Apparently, they don't have much of what they advertise in stock.
- 4D Model Shop "They have a proper shop with racks of sheet material. They also sell the tools and laser cutting services. A quicker way of getting sheet material, but you'll probably have to cut it yourself."
- http://www.trentplastics.co.uk/ (have dealt with them, Levi was very helpful get the order in before 3pm and they'll dispatch it next day, plus if you don't see it on their website call and ask as they have more in stock than is on there)
- Wonderful service from Tomas over at www.1plus2d.com just up Kingsland Road, at relaxed £20 /hr. He's got a HPC 600x900 bed. Top guy, very helpful! -DanC
Others to try: Not a recommendation, just is just a list of places we've found nearby.
- http://www.cutlasercut.com/ (Vauxhall)
London retail or trade counter
- RS has most things, more professional. 4 london trade counters, including one in Bow
- Cricklewood Electronics A real shop, with little drawers of stuff & everything.
- Maplin chain, more hobbyist. Getting really poor at actual components.
- Cool Components Sparkfun stuff. Personal callers now allowed by appointment.
- Earthshine Electronics Run by a Hackspace member. Arduinos and other parts (can always be found on hackspace IRC) Discounts for LHS members on request.
- Direct Electronics (Manor Park) One of the few remaining component shops that isn't Maplin. Not visited for years but they seem to still be there.
- Display Electronics Possibly the last remaining electronics surplus place in London.
- Retail site for the Scientific Wire Company - unusual wire : enamelled, knitted, litz etc.
- Oomlout for some easy Arduino starter kits
- Search ebay for nearby auctions ending soon
- Clerkenwell screws All manner of screws etc. and some tools Wholesale Division of Clerkenwell Screws which has product lists
- Networking infrastructure
- Paintworks Nearest to the Space, on Kingsland Road. Don't know anything more about it Akki14 (talk)
- Atlantis Art is a large warehouse-sized art shop with all kinds of things. Probably not cheapest for things like liquid latex, silicone moulding materials etc but it's there and it's reasonably priced for large sheets of paper, melinex (laserable clear sheet - useful for stencils), higher quality art supplies etc. Not too far of a walk from the Space on a nice day.
- Cass Art nearest branch is probably Islington. The "large" shop in Islington isn't as big as Atlantis. Range is slightly less upmarket than Atlantis as well. Know your prices before going - a lot of it claims to be cheaper than retail but actually isn't cheapest available elsewhere.
- Cornelissen & Son Holborn area. Pretty shop. Stocks some interesting papers, vellum, parchment, etc but take a shopping list with you if you're buying anything other than standard packs of papers as their paper stock is hidden away downstairs. Can be a bit on the pricey side but check out their clearance section for decent priced artists brushes.
- London Graphics Centre Covent Garden area. Useful for obscure graphics things. Prices are a little on the high side but generally they have higher quality materials anyway.
- Cowling & Wilcox branches nearest/easiest to get to from the Space would be Shoreditch High Street & Soho. A mix of art supplies and craft supplies. Middle of the road for quality/prices.
London-based, primarily mail order
- Earthshine Electronics Ran by a Hackspace member. Arduinos and other parts (can always be found on hackspace IRC) Discounts for LHS members on request.
- Robosavvy Robotics, Sparkfun, Makerbot spares. Popular online forum for humanoid robot enthusiasts (mail order next day delivery)
- skpang S K Pang - Sparkfun products and other parts
- E M A Model Supplies Plastic weld solvent, plastics, casting, tools
- S&M Tools & Hardware Hand & power tools for model making, engineering, jewellery, DIY, etc.
- Farnell has almost everything, more professional. Owns CPC and Newark. Note CPC are sometimes cheaper than Farnell for the same items
- RS has most things, more professional, usually more expensive (especially for small orders).
- Rapid Usually cheaper than RS or Farnell for run-of-the-mill parts. Website search often sucks - try to get a paper catalogue
- Mouser USA based but free shipping. >£50 Like farnell but often a little cheaper.
- Digikey USA based but free shipping >£50. Like Mouser but bigger range, typically a little more expensive
- Toby UK Specialising in board-board and signal-board connectors. Potential UK supplier of hard-to-find extra long pin headers as used by the Arduino platform.
- Northern Connectors Specialist connector distributors. Mainly bulk deals but order threshold is low.
- Seeed studio
- Sparkfun electronics
- Alibaba great for bulk orders from China
- Tindie - electronics marketplace like Etsy
- Oomlout Arduino & DIY electronics
- Amazon (next-day with Russ's Amazon Prime account) - equipment is often cheaper
- Bits Box
- Hobby Tronics Yorkshire based well sorted mail order, sparkfun stuff, their well made own versions and components.
- Barend Hendriksen Holland. Interesting RF parts.
- Keytronics Obsolete IC supplier mail order, can also be found with small parts at radio rallies.
- MMS Electronics - SPI/I2C graphic LCDs (pricelist)
- Metals4u Metal stock, Aluminium, Steel etc. - Welding equipment.
- Hindleys Stock metals and plastics, and most kinds of tools and consumables, often surprisingly cheap
- Mega Electronics PCB-making supplies. Their products are also sold by Farnell and Rapid but may be cheaper from Mega.
- Smtstencil Cheap polyester SMT stencils. Quick service.
- Chronos Engineering supplies, tools etc. - Have showroom in Dunstable (5% discount but some things need to be ordered in first)
- Modelfixings Every type of nut, bolt etc. you can imagine, including very small ones.
- Fix8 Like 'Modelfixings' but more cost-effective for large numbers.
- A2A4 Stainless fasteners, screws etc.
- TechnoBots - electronics and some very nice hardware components, gears, pneumatics, chains, pulleys (10% Hackspace Membership discount code available - contact asc/ascen on irc)
- Goodwill, Ultraleds, Led-tech - A gazillion kinds of LED
- Sure Electronics (China) Interesting selection of electronic stuff.
- Mindsets Online formerly MUTR Various interesting stuff mostly intended for school science labs
- Cole Parmer - chemical equipment
- HS Walsh Jewellers tools and supplies.
- Beers of Europe, King's Lynn A truly amazing selection of beer.
- RDG Tools - machine tools and accessories, free postage, generally reasonable prices.
- Reeves model engineers - metals etc.
- GLR Distributors - metals, steam engines, tools. Geocities-style website.
- Allendale Stores I first came across this company at a model engineer's exhibiton, trading as Machine DRO and selling cheap glass scales and display units. They now seem to have branched out into a complete hacker's delight - SMD rework stations, RC data loggers, machine tools, wifi aerials .. all those chinese things at more or less chinese prices, but in Hoddesdon. One to watch.
- MetPrep Supplies hard to find wet/dry sanding belts used in preparing metallurgical samples and what the belt sander was originally used for
- Camden Some fairly unusual books (by no means all about steam)
- Shapeways 3D printing company using laser sintering. JimM uses them a lot.
- Cut-tec 3d metal fabrication
- Ciseco Microcontrollers, radio modules, Raspberry Pi expanders
- Westfield Fasteners Nuts & bolts
- HacMan's suppliers list
- The College Engineering Supply Primarily a mail order service for model engineers. Materials for casting, sheet metals, tubing, tufnol, etc.
- Direct Plastics various plastic supplies including PEEK
- Zapp Automation CNC components - steppers, bearings, ballscrew etc
- Astro Media Educational scientific items
- Proto-pic good for soft-circuits stuff and various electronics
- Engineer's Mate bearings, fixings, all sorts of mechanical bits. also on ebay.
- Gimson Robotics nice motors and gearboxes
Although homemade PCBs have been succesfully made in the hackspace, there are occasions where commercial suppliers are more convenient - where you want larger numbers, or very detailed etching, or the advantages of solder resist, silk screen etc. There are several possibilities :
- UK/EU commercial suppliers. Fairly expensive but can be fast and good quality.
- Spirit Pretty well priced. Also provide a free & fast 'Naked' PCB service 
- Stickleback "offers a good low cost pcb service for 2 layers PTH provided that you don't want less than an 0.6mm hole size and an 0.2mm wide track or feature"
- Eurocircuits EU based PCB house - several proto services. Fairly cheap for stainless SMT stencils.
- PWT UK based full-capability PCB place for stuff Screenbond can't do. Typically cheaper than Eurociruits for 4-layer
- Screenbond UK based PCB house with unusually low tooling costs (typ £40). 1 & 2 layer only. Can do 24hr turnround if you have deep pockets.
- PCB-Pool Proto/low-volume oriented PCB service, not the cheapest these days but offer a free stainless SMT stencil.
- PCB Train Fast turn around, good prices. Also have an assembly service and a 1 day (~£40 all in) prototype service for uncoated 2 layer boards.
- Far-eastern commercial suppliers. Probably cheaper for really large batches
- PCBCART PCBs from China. Very cheap once you get over a square foot or two. Reliable, Quality generally good. A gazillion options - funky resist & silk colours (Matt black is cool!) , thicknesses etc.
- Far-eastern hobbyist suppliers such as Seeed Studio.
- Community cooperatives such as DorkbotPDX combine designs from multiple users to make an economic panel, then split it up.
- Aluminium Warehouse Seems to have a good selection and very very good prices (and prices listed on the website!).
- Metals4U Good selection of metals (including brass etc), and reasonably priced. Prices listed online.
- Doré Metal Services Relatively cheap and good selection. Have to call/email for quote though.
- Orion Alloys Moderately priced, but the prices aren't listed.
- Smiths Metal Centres Have physical presence in london (N1 4BZ) but very very expensive. Avoid.
- Noggin End metals
- CPM, Birmingham - no review
- Metal Stock t: 01977556515 Very helpful & friendly. Good selection & prices.
Other localish possibilities:
Laser Cutter consumables
Go to Four Vintners - it's "about 25% cheaper than Majestic" and closer. Don't waste the beer money on the local offie (although they are friendly and helpful).
Kris Wines, Camden - Belgian, Bavarian and British beers
See biohacking suppliers
If you're looking for second-hand hand tools, the following lists were culled from a mailing list post and other sources. Feel free to add detail if you check any of these places out.
In the London Area
- C. Demetriou Zingas is a DIY shop that sells power tools, timber, paint and piping. They also sell some second hand items. Open hours seem a bit unpredictable, so might be worth calling first.
- Brick lane - theres a small but tardis-like 2nd hand/antique store just off the top of brick lane, on the west side - possibly Bacon Street - in there you will find a massive selection of old and used hand tools.
- Workaid has a shop in Chesham. They mostly send tools to developing countries, but also sell a lot of them off on site. These are all refurbished/sharpened, since that's what they do, but they're also always looking for volunteers.
- Peetamber from Tools For Self-Reliance comes over to the hackspace around once a month. He's always got a nice selection of older hand-tools, usually of excellent quality. He usually announces on the mailing list when he's coming over.
- There is a guy who's sometimes at Greenwich Market or Spitalfields Market with old tools
- There are tools second hand, as well as new tools at reduced prices, sold at Nine Elms Sunday Market, Vauxhall, SW8 2LF
By mail order
- Antique Tools
- Second Hand Tools, also have an outlet in the antiques village on the promenade in Lyme Regis.
- Tool Bazaar
- Stewart of Reading Surplus electronic test equipment
Classified ads and junk sales
- engineering machinery , materials and small ads
- amateur radio rallies have lots of interesting junk and random components. Rallies have been in decline in recent years, but Dunstable Downs near Luton in May is always worth a trip.
Some online sellers offer distributor prices to hackspaces provided a minimum order level is met.
- Dangerous prototypes
- Earthshine Electronics Discount to Hackspace members on request
- Technobots 10% Hackspace Members Discount (email asc / ascen)
If you're interested in aggregating your order to obtain these discounts please provide details
Castle Fine Arts Foundry (bronze casting): free wax - click green 'free wax' icon top right of page.
Things we might want 
I have dealt with these on ebay and received from good to outstanding service from them
- the solderman soldering equipment (artag)
- acuflow syringes (artag)
- crodnet components (artag)
- Spiratronics components (artag)
I have dealt with these sellers in the real world (and sometimes also on ebay) and will gladly use them [again].
- pyedpyeman surplus radio gear (artag)
- fazerblazer machinery and manuals (artag)
- nezretroussez components and military radios (artag)
- pcefficient ex-corporate IT equipment (artag)
These sellers seem to have particularly interesting and relevant products, but I haven't dealt with them yet.
- vinyl cutting blades (artag)
- John Stevenson from rec.models.engineering (artag)
- gas-filled tubes (artag)
If you need somewhere to hold an event, the hackspace may be suitable. See Guides/Planning an event for some notes about how to organise an event at the hackspace. If the hackspace is too small, or booked up, or inappropriate in some way, : here are some useful suggestions (unwieldy pdf).