This controller from 60Beat will give you a gaming experience on your iPad.
Gaming is usually a lean-back situation, with hands on a controller and back against a cushion. With 60-Beat's plug-in controller, the iPad just got "gamier."
The controller uses the headphone jack to control one of two available games: Aftermath and Bugdom 2. For sound purposes, it comes with a splitter. So, it does take away the touch-screen capabilities of the iPad, but it also offers that lean-back, hands-on controller experience.
For $50, that may not be enough games to cause critical mass for sales, but, as The Next Web points out, you can't stash an Xbox 360 in your backpack and play on the train.