Read recently.

Introduction to Algorithms by Cormen et al. (I've read about halfway through this, excellent reference, not so good of a starting point).

Structure and Interpretation of Computer Programs (SICP) by Abelson et al. - Available for free (legally) right here

Algorithm Design Manual by Skiena - A much better starting point than "Introduction to Algorithms"; very useful, too.

The C Programming Language by Kernigham and Ritchie - A perfect model of what a programming language tutorial should look like

Learn You a Haskell for Great Good by Miran Lipovača - Written in an entertaining fashion, the illustrations are quite nice and explanations are awesome. Available for free (legally) here

Impatient Perl by Greg London - Teaches you Perl in a couple of hours so you start hacking together scripts, available here

Problem Solving Strategies by Arthur Engel - Absolutely amazing book with a great collection of mathematical puzzles

Anything by Martin Gardner - Almost always a fun and entertaining read for anyone

Linear Algebra by Gilbert Strang - Very conversational textbook about Linear Algebra

Principles of Mathematical Analysis by Walter Rudin - A classic, very clear explanations, great proofs

Fermat's Enigma by Simon Singh - A very entertaining read about Fermat's Last Theorem, but, if you're looking for something technical, this definitely isn't it