As the summer has been wearing on, I've thought more about this whole "cluster" thing and I've decided the first project I want to do is a game of 21 (poker) which uses the standard rules and have the "player" adopt the same rules to play as the house, but with a slightly higher limit on the hand. Could also do some simple "card counting" techniques that I think most people could pull off (such as number of aces played, and then maybe working up to number of face cards played etc). Practical use, and easy to program up.
Now if I only had a cluster..