Another board I frequent has a thread like this (didn't find one here), it's a pretty handy way to find new useful apps without browsing the store. I've noticed that a lot of the most popular apps often have some terrible reviews, so finding the best ones can involving a lot of searching.
My favorites thus far:
Bloomberg: Good replacement for the Stock app that comes on the Phone, presents a lot more information in one place. Just got a major update, and it's even better now.
Simplify Media: Stream your home music library, perfect if your music won't all fit on your phone.
Air Sharing: Just got this yesterday but so far it's pretty awesome. Mounted the iPhone on my home computer as a disk and transferred files onto it. View PDFs and Excel files with no problem so far.
LOLCats: I like LOLCats
I am waiting to see if Netshare comes back, but I doubt if apple/AT&T will allow it.
Games discussion previously started here:
http://ducatimonsterforum.org/index.php?topic=7754.0 (http://ducatimonsterforum.org/index.php?topic=7754.0)
Non-game faves of mine include:
OmniFocus - http://phobos.apple.com/WebObjects/MZStore.woa/wa/viewSoftware?id=284885288&mt=8 (http://phobos.apple.com/WebObjects/MZStore.woa/wa/viewSoftware?id=284885288&mt=8)
Pandora - http://phobos.apple.com/WebObjects/MZStore.woa/wa/viewSoftware?id=284035177&mt=8 (http://phobos.apple.com/WebObjects/MZStore.woa/wa/viewSoftware?id=284035177&mt=8)
Air Sharing - http://phobos.apple.com/WebObjects/MZStore.woa/wa/viewSoftware?id=289943355&mt=8 (http://phobos.apple.com/WebObjects/MZStore.woa/wa/viewSoftware?id=289943355&mt=8)