My good buddy Alexander Pick is about to release the full Quake 3 Arena for iPad today, with on-screen key controls, like it should be. You can play offline and online, and add levels through iTunes file sharing, using drag-and-drop.
Unlike the crashy iPhone version and the fake iPad video that made the runs a while ago, this one is very real. It runs smoothly at 1024 x 768, even with the 4.2 beta, has iTunes integration for file sharing, on-screen controls, and it looks great, especially if you download the high resolution texture files from here. The only requirement: Jailbreaking your iPad (which is easy and painless).
Alexander tells me he's working on Bluetooth Keyboard support, but there's a problem with Apple's code at the moment, that needs to be fixed for the acceleration to work (if you have ideas, contact him through the forum at Paduser).
The application should be available within the next few hours in Cydia, and you can get support and the GPL code at [Paduser]