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).