The C Programming Language by Brian Kernighan and Dennis Ritchie. This primary text is also known as "K&R" and gives a terse but powerful introduction to C. This book is for beginners, but don't get discouraged if you find it difficult.
SCJP Sun Certified Programmer for Java 6 Exam 310-065 by Kathy Sierra and Bert Bates. One of the understated benefits of certification is that you have to learn corners of the subject you don't use everyday. This book helped me learn Java much more thoroughly than before. If you are looking to build your Java knowledge and skills outside of a formal computer science education, or just want a certification for your resume, then I highly recommend this book. Sierra and Bates recently published a book for Java 7 that I own but have not yet read. These books are good for the intermediate programmer with some experience with the language.
Java Puzzlers by Joshua Bloch and Neal Gafter. This entertaining read deepens understanding of bizarre errors, regressions, and corner cases in the Java language and reinforces the lessons taught in EJ. This book is not for beginners.
Contemporary Calculus by Dale Hoffman. An incremental, approachable, free Calculus textbook with lots of proofs and applications.
CISSP All-in-One Exam Guide, 6th Edition (aka "CISSP AIO" or even just "AIO") by the late Shon Harris. This humorous text covers a massive scope of Information Security topics. The concepts and vocabulary touched upon in this text should be a common language for all serious technologists. Basically every developer, engineer, technician, and manager in the field needs to read this book.
CCENT/CCNA ICND1 100-101 Official Cert Guide by Wendell Odom. I read an earlier version of Wendell Odom's ICDN1/CCNA books. I strongly recommend them - particularly the ICND1 textbook. I know that I'm biased since I work primarily in networking, but I believe that everyone who works in the communications industry, including management and sales, should take (and pass) the CCENT exam. Wendell Odom's books are quite verbose and thorough, which should practically guarantee the estudious reader success on the exam and a strong introduction to networking. As an aside, I would urge anyone planning to take Network+ to just go for CCENT (ICND1) instead. Same material, slightly more prestigious, cheaper, and CCENT feeds directly into Cisco's vast world of technologies.
The Ugly American by Eugene Burdick and William Lederer. Required reading at most USG agencies and recommended to all US citizens traveling overseas.
On Killing: The Psychological Cost of Learning to Kill in War and Society by LTC(R) Dave Grossman. Every current and former military member and policeman should read this book. (Note: if you've find this page and are waiting to go to basic training, get off the internet and go run! You'll have time to read later.)