My favorite apps:
Byline - RSS Reader that syncs with Google. It's nice because it will cache all the articles and their HTML pages so you can view them anywhere.
Air Mouse Pro - This works as a virtual mouse/keyboard for Windows or OS X. It's really nice and I use it on my Hackintosh Media Center to help when I have to click on dialog boxes, or type a password in.
Mobile Fotos - An app for Flickr. This has a great interface, caches the photos that you look at, and allows you to edit/upload new ones right from the app itself. I like Mobile Flickr site, but for $3, this is much nicer to use.
Phone Flix - Organize your Netflix queue (Instant and delivery)
Photogene - Like a little Photoshop on your phone.
OmniFocus - I loved using Things, and The HitList, but this is nice because it syncs via WebDav or MobileMe, so I don't have to be on the same wireless network. I can sync while I'm away and know that I'm going to have the same lists when I get home.
TV Forecast - You add shows to your list and it will show you when new shows are coming on that week.
Yelp! - Great for finding restaurants, etc...
... and a few more I really like
The Weather Channel
Textfree
Wikiamo
Tweetie/Twitteriffic - I go back and forth
1Password
Pano
Pandora
Overall, there are so many apps... hah.