Tech writing:

• The Tech Writing Game: A Comprehensive Career Guide for Aspiring Technical Writers by Janet Van Wicklen
• How to Communicate Technical Information: A Handbook of Software and Hardware Documentation by Jonathan Price
• Managing Your Documentation Projects by Joann T. Hackos
• Designing and Writing Online Documentation by William K. Horton

Graphic design:

• The Visual Display of Quantitative Information by Edward R. Tufte
• The Non-Designer's Design Book by Robin Williams

• The Microsoft Manual of Style for Technical Publications

• Learning the vi Editor by Linda Lamb, Arnold Robbins
• Learning the Unix Operating System by Jerry D. Peek, Grace Todino, John Strang
• Essential System Administration by Aeleen Frisch
• Unix System Administration handbook by Evi Nemeth

Programming (emphasis on books that teach you to read it without hands-on work):

• C: The Complete Reference by Herbert Schildt
• Perl for Dummies by Paul E. Hoffman AND Mastering Regular Expressions: Powerful Techniques for Perl and Other Tools by Jeffrey E. Friedl, Andy Oram (Trust me, you really need both books.)

Protocols:

• Internet Email Protocols: A Developer's Guide by Kevin Johnson

• HTML & XHTML : The Definitive Guide by Chuck Musciano, Bill Kennedy