Occasionally when I'm doing weird algorithmic stuff I end up with my nose in one of these books, combinatorial algorithms more often than many others.

I'm a big fan, but I think you already have to be pretty deep into the world of algorithms and discrete math to get a lot out of them. I cheated my way into that world by starting my math minor a few years ago with Combinatorics, specifically because I felt like learning how to count things in weird ways would help my autrocious mental math (it did!).