Tom7 (the author) has done quite a lot of great stuff; his game "T in Y world" [1] is pretty good, and you may also remember him from his programs Learnfun & Playfun, which taught themselves to play Super Mario (and various other NES games) [2].

Do check out more of his work!

[1] http://tinyworld.spacebar.org/ [2] http://www.cs.cmu.edu/~tom7/mario/