One-Handed Game Controller

So basically I have an idea in the back of my mind about a game controller that attaches to the Tablet PC allowing you to use it like a Gameboy. When I was in Japan, I found a game controller designed for use in one hand. However, I have not had an opportunity to really use it since I don't play any games that use a game controller. It's just one of those things that seem like they would be useful until you realize you wouldn't really use it. But now that I have a utility that allows me to use it with any apps I think it will come in more handy.