These are some games I've designed that are print-and-play --- you can make your own copies and try them out.
Double Blind Winner of 2005 about.com game design contest
Prisoner's Quadrangle A 4-player variant of the classic Prisoners' Dilemma, with a few thoughts on its applicability to real-world situations
Prisoner's Quadrangle Essay A whole lot more thoughts on Prisoners' Quadrangle
Here's one more: Operation Fishtank, an idea I had for a computer-generated evolution simulator. If anyone would like to collaborate on programming it with me, get in touch!