I've tried only 3 apps so far, though I read through the descrips of most of the Free Apps.
Shazam: This listens to a song for 15-20 secs and tells you what the song is. I only demo'd with one song which it got correct, but reviewers say they've had fantastic results. This is excellent.
ePocrates: Registration is evil, they want to know your name, which medical school you went to, what year you graduated, and they attempt to VERIFY that you went there. Ick. But otherwise, impressive and important app for health workers. The download is actually an install app which then installs the larger entire application. So don't be fooled by the 0.7 mb file size.
Tap Tap Revenge: This is a well done game (and free) with tapping and shaking to music. The downside is that they're pre-done music so it can't take music from your library. I expect they'll add that (possibly for a fee?) since they had it in a previous version apparently. There's even a two player version and a contest today and tomorrow with a $300 gift certificate prize.
Yes there are a LOT of silly apps on the iTunes store (sim stapler, white screen flashlights, bubbles, pretend beer/milk, lightsaber sound on movement). I haven't downloaded any because I don't want to crud up my iPhone. But they look like fun 🙂