To answer your question specifically: the best book for learning math as it applies to computing IMHO is Concrete Mathematics by Graham, Knuth, Patashnik. The name is a pun on "Discrete Mathematics". (It's also one of the most beautifully typeset books I've ever seen.)

If you want to stretch your mind about computing, then I'd highly recommend Structure and Interpretation of Computer Programs by Abelson and Sussman. An online version of the entire book is also available. The examples are in Scheme, but don't let that deter you. It's great stuff.