Over at club.live.com, they've got several "ticket games" going on. Spend an hour or two playing, and you can get items ranging from song downloads to headphones all the way up to an Xbox 360.
The game with the highest ticket value is called Flexicon, however they didn't really test their game data very well.
Here is the correct solution marked incorrect.
Here is what they think is the correct solution.
Remember, you may have a bug-free game engine, but bugs in your data will frustrate your users worse than a crash many times. Especially for games, the rule of thumb is that you generally spend over two thirds of your time testing the data.
If you aren't testing your data, you aren't testing your game.