Books, writings, essays

Books online, computer related

• The Art of Unix Programming by Eric Raymond
• The Jargon file
• The Tao of Programming
• Free as in Freedom: Richard Stallman's Crusade for Free Software
• Hackers (chapter 1 and 2) by Steven Levy
• How to think like a computer scientist: Learning with Python
• Structure and Interpretation of Computer Programs
• Historic documents in computer science and engineering
• MIT OpenCourseWare
• Open Source: Voices from the Open Source Revolution
• O'Reilly Open Books Project
• Structure and Interpretation of Classical Mechanics
• The Craft of Text Editing (or: Emacs for the modern world)
• E.W. Dijkstra archive
• Atari Archives: Digital Deli, Creative Computing, Machine Language for Beginners, Creating Adventure Games, etc. Mostly Atari-related, obviously by the name.
• Programming Language Texts online
• A New Kind Of Science Online (Stephen Wolfram)

Books online, not computer related

• The Little Prince by Antoine de Saint-Exupery
• Fanny Hill

Articles, writings, essays

• The cathedral and the bazaar: influential open-source essay; see also Homesteading the noosphere and The magic cauldron
• The Unix koans of Master Foo

Collections

• Project Gutenberg

On Writing

• 10 tips on writing the living web
• Ten Mistakes Writers Don't See (but can easily fix when they do)
• The Elements of Style

Manuals

• Subversion: The Definitive Guide
• Old computer manuals