Library

In the space

Electronics

• Foundations of Analog and Digital Electronic Circuits, Anant Agarwal & Jeffrey H. Lang
• The Principles of Computer Hardware, Alan Clements

Security

• Applied Cryptography, Bruce Schneier

Natural/Spoken Language

• Step By Step in Esperanto - For those who like their languages easy and constructed.

On the web

Machining

• Guerrilla guide to CNC machining and resin casting:

Volume 1: Basic theory and preparations

Volume 2: Real-world projects

• Machinist's BBS

Electronics

• The Giant Internet IC Masturbator (IC pinouts without pages of ads)
• Native USB for AVR
• Analog Circuit Design: Art, Science and Personalities (superb book about analog design edited by Jim Williams)
• The Art and Science of Analog Circuit Design (more in a similar vein)
• http://code.google.com/p/arduinoshiftreglcd/