General Documentation Sites:

• O'Reilly Network Safari Bookshelf

Open Source Culture and Business:

• The Cathedral and the Bazaar (Actually, all of the writings of Eric S. Raymond)
• Open Sources: Voices From the Open Source Revolution (Open Source Book)
• Free as in Freedom: Richard Stallman's Crusade for Free Software (Open Source Book)
• O'Reilly Open Books Project (List of O'Reilly books available under Open Source license)
• O'Reilly Open Source Bibliography (stored locally)

Quick Reference Cards

• Apache Reference Card (stored locally)
• Perl Reference Card (stored locally)
• XML Reference Card  (stored locally)
• XSLT Reference Card (stored locally)

General GNU/Linux Documentation

• Red Hat Manuals  (stored locally)
• GNU Manuals Online
• The Linux Documentation Project
• Josh's Linux Guide
• Mike's Linux Cookbook
• Linux Network Administrator's Guide (Open Source Book)
• My Linux Crib Sheet (stored locally)

Server Applications:

• Apache Manuals (stored locally)
• Using Samba (Open Source Book)
• MySQL Reference Manual (stored locally)

Client Applications:

• Creating Applications with Mozilla (Open Source Book)

XML Document Processing:

• DocBook: The Definitive Guide (Open Source Book, stored locally)
• DocBook: XSL Stylesheet Reference (Open Source Book, stored locally)