There have been image stabilization iPhone camera apps before, but not until 3.0 have they had adequate access to the hardware to do proper processing. Pro-Camera is one of these.
Pro-Camera's features include that anti-shake, which uses the accelerometer to detect where the iPhone is moving in space, as well as self-timer and digital zoom. It's $3, which is not that much if the app really does improve your images dramatically. Though, they should really have some kind of demo that lets you take 10 photos to see if you like it. [iTunes via Wired]