(Obligatory: http://www.xkcd.com/974/ http://www.xkcd.com/974/ -- but Knuth solved the arbitrary condiments problem, and others besides.) The Concrete Mathemat

(Obligatory: http://www.xkcd.com/974/ http://www.xkcd.com/974/ -- but Knuth solved the arbitrary condiments problem, and others besides.) The Concrete Mathematics book that resulted was a masterpiece in my opinion. I learned so much about how to computationally do discrete math from that book. And it's a very elegant package.