I don’t expect this to get many replies, seeing as it’s not only about math, but most discrete math students’ worst nightmare, combinatorics, but it’s worth a shot, I guess.
Well, to make this as short as possible, I finished my Discrete Math II course last semester, and have become totally wild about combinatorics, so much so that I’m taking a graduate course in the class next spring. I know the basics-- permutations, combinations, the pigeonhole principle, ramsey theory, and I’d really like to obtain a more in-depth understanding of everything, and to play around with more difficult problems then were covered in my class.
Most of the books on Amazon are really pricey, so sadly I’ll probably only be able to get one, and I’d like to make sure it’ll be useful. Can anyone help this pathetic geek out? 
Have you seen Concrete Mathematics, by Donald Knuth et al.?
Do you have any background in abstract algebra? A lot of advanced combinatorics uses group theory, so it would behoove you to have some familiarity with that.
As far as an actual combinatorics book goes, I can’t give any specific recommendations. However, I can point you to Dover’s site, where they offer a complete catalogue of their paperbacks, very few of which are more than $20. You can probably find something there.
Thanks, guys! I’m checking out Concrete Mathematics on Amazon right now, and Dover’s selection looks really promising. ultrafilter, I think you’re right-- I ought to read up on group theory. I’m dropping by Borders tomorrow to browse their selection-- I think it might be a good idea to read some math books IRL to make sure they’re clear and give good examples before buying anything online.
Thanks again!
Clear? Math books? 
The book I used for algebra was Israel Herstein’s Topics in Algebra. I recommend anything else in place of it–it’s not a good book for self study. Find something that concentrates on group theory, as that’s probably all you’ll need. Ring and field theories are fascinating, and if you want to go real far in computer science (you are in computer science, right, cercaria?), you’ll probably run into that kind of stuff, but you don’t need to know them now.
Also, please let me know what combinatorics book you do settle on. I want to learn more, and I figure you’ll pick a decent one. e-mail’s in my profile.
The book we used in grad school was Combinatorial Mathematics by Herbert John Ryser, but it’s been a long time since that class, so I don’t even know whether it’s still in print.