Like Erica, I've been poking around the App Store all morning. Unlike Erica, I'm not brave enough to install the firmware without the official word from Apple, but in the meantime, here's a few free apps in there that are definitely worth a download right away.
Advent: A free version of Colossal Cave Adventure, on the iPhone day one.
Phonesaber: Yes. This is exactly what you think it is. And it's free.
Light: Don't spend money on one of those other flashlight programs -- get Erica's original for completely free. (In fact, you might as well go ahead and get all of her apps, they're all great.)
MixMeister Scratch: Free vinyl scratching over your iPod touch or iPhone's background music. Silly, but fun for aspiring (or, more specifically) wannabe DJs.
Zenbe Lists: A pretty good-looking free alternative to all the other To-Do applications out there.
???: I have no idea what this is (looks like some kind of Memory-type game), but it's free and it's hilariously beautiful. Update: Actually, this looks like the non-English version of Jirbo Match. But still, it looks like amazing and colorful fun.
NetNewsWire: This and AIM aren't really hidden, but they're must-haves, of course.
Have more that you've seen? Link us in the comments. I may not have the ability to install apps on the phone yet, but when I get it, I'll be ready.