If you like playing games, why not test your mettle against some game AIs?
Better yet, create your own, and test it against the other AIs, or see if you can beat the AI you created.
This is all still a work in progress, with Rock-Paper-Scissors being the proof of concept, which is currently playable, but still some work to do.
Next up is Tic-Tac-Toe, followed by more games and more features.
Might take some time to get a Grandmaster chess AI to beat Deep Blue up and running though.