[synthmeat]

I'd second the "What is Mathematics?" and "Mathematics: Its Content, Methods and Meaning" recommendations, in that order. Both are very cheap, comprehensive, and in ascending rigour. After those, it's really dealer's choice, with "Concrete Mathematics" being of particular interest to computer scientist.

Additionally:

- "Princeton Companion to Mathematics" is really fun to have around for exploration

- if you're really really rusty with math, take a week or two with "Mathematical Handbook - Elementary Mathematics" by Vygodsky

I literally have all these on my desk at this very moment, what a fun coincidence.