There are now a few different iOS peripherals to choose from if you're looking to add physical controls to your near-buttonless Apple device, such as the iCade, the Gametel add-on, and the iControlPad.
Unfortunately, they all suffer from one rather large flaw: a dearth of compatible titles. That may be about to change.
Developer Matthias Ringwald has released a new Cydia application for jailbroken iOS devices called Blutrol, which lets you map the iControlPad's physical buttons to virtual on-screen presses.
In other words, it makes the iControlPad compatible with almost any iPhone, iPad, and iPod touch title, including the likes of Grand Theft Auto 3, Death Rally, and the recently released Super Crate Box.
At present, Blutrol only works with the controller's iCade mode, which means analogue controls are still out of bounds. However, this functionality is already "on its way".
Check out the iControlPad website for more info.
Thanks to Chris Lewis for the tip.