The Magic of Math: Solving for x and Figuring Out Why cool new book!
Secrets of Mental Math: The Mathemagician's Guide to Lightning Calculation and Amazing Math Tricks lightning arithmetic!
The Book of Numbers beautiful and accessible
The Shape of Space (Chapman & Hall/CRC Pure and Applied Mathematics) topology that will stretch your mind
A Mathematical Mosaic: Patterns & Problem Solving a cool book with lots of fun facts
Proofs from THE BOOK elegant proofs at an advanced level
Which Way Did the Bicycle Go?: And Other Intriguing Mathematical Mysteries (Dolciani Mathematical Expositions) a fun set of challenging problems
Proofs without Words: Exercises in Visual Thinking (Classroom Resource Materials) (v. 1) proofs by picture!