Math for hackers.
smanek: As a really high level overview of math, I like The Princeton Companion to Mathematics (or the ~1/4 I've made my way through so far). It's a bit too abstract though - it covers an immense amount of material so they have to be - but I still feel like something is missing.My 'overview of math' is probably The Road to Reality (which is ostensibly about Physics, but really spends just as much time talking about math) - which is a little bit more hands on and concrete. It makes a bit tougher to get through (difficulty, and quantity), but I think it's worth it.