Check out Interviewing at Microsoft . A few particularly interesting ones can be found here . Ease your way into it with a simple introduction or some combinatorial geometry . For definitions of many combinatorial terms, see the Dictionary of Combinatorics . To delve deeper, check out the Electronic Journal of Combinatorics .
Poker is an excellent source of combinatorial problems.
Refresh yourself on the rules , then check out some poker probabilities . Also seen in today's lecture was a basic intro to injective, surjective and bijective functions. See a nice introduction to the topic, or read about the beginnings of set theory. If you like Java applets, you should also explore the permutation resources at Cut the Knot. One use of combinatorics, as we found out in lecture today, is counting anagrams.