These are books that most computer programmers should have. If you need to know about the topic, you can buy the book sight unseen, and know that you will not be disappointed.
EssentialThe C Programming Language, 2nd Ed. Unix Network Programming, 2nd ed. (rec. by elim) Salas and Hille's Calculus (rec. by elim) Algorithms in C (rec. by elim) Abelson and Sussman: Structure and Interpretation of Computer Programs Foley, van Dam, Feiner, and Hughes Stevens: Advanced Programming in the Unix Environment (rec. by josh) Camel book Hennessy and Patterson: Computer Architecture, a Quantitative Approach Tufte: The Visual Display of Quantitative Information Writing Solid Code Feynman Lectures Bruce Schneier: Applied Cryptography, 2nd ed.
These are good books. If you really want to know the subject in detail, go and get them.Advanced Perl Programming Java in a Nutshell, 1.1 ed (already obsolete, sadly) Deep C Secrets (rec. by yosh) Unicode
What's your experience? Do you have a favorite essential book? Send me a cite and a brief review of why the book merits listing here.