Air Sharing: Enables you to use wifi to copy files from your computer onto your iPhone.
AP Mobile News Network: Great news app.
Bloomberg: Excellent stock news app. Think of it like the iPhone Stocks app on steroids.
Crosswords: Robust crossword app with ability to download a variety of free puzzles.
Equivalence: Calculator with conversion functionality. Very handy!
Fizz Weather: Excellent weather app that includes radar, 2-day & 5-day forecast, etc.
i.TV: New (and very well done) app that downloads your local movie and TV listings.
iChillout: Relaxation sounds with timer.
iGas: Gas prices for nearby stations.
iZen Garden: Sand garden with relaxing music.
Koi Pond: Beautiful koi fish pond with relaxing music (not practical by any means, but very elegant).
Meditator: Meditation app (timer & meditation sounds).
MyDelicious: Lists your delicious bookmarks.
Newsstand: Very cool RSS reader that displays feeds as magazines on rack.
Pandora Radio: My favorite radio app. I love Pandora’s Spa radio.
Photogene: Excellent photo editing app.
ReMovem (free): Basic but fun game.
Solebon Solitaire: Solitaire game suite.
Stanza: Excellent ebook reader.
Twittelator Pro: Twitter app (can view by replies, all friends, everyone, search, etc).
WhitePages Mobile: Includes business search, people search, and reverse phone directory.
WordPress: Great for publishing to one’s WordPress blog while on the go.
WriteRoom: I use it to create notes to myself. More robust and elegant than the default notes app.
WunderRadio: Excellent radio app – lots of radio stations. (I use WunderRadio to listen to CNN-TV on my phone.)