As requested, here’s my essential iPhone Apps:
In alphabetical order

Air Sharing
$4.99
Let’s your iPhone be mounted to your desktop like an external drive. Not sure why this isn’t normal behaviour, but this works fine.

Amazon Mobile
Free
Buy, compare, shop, wishlists… indispensable when you’re a cheap bastard like myself.

AOL Radio
Free
I’m not a radio fan at all, but find myself listening to this every so often. Stations around the world and a batch of very specific stations (Classic Punk and All Clash being two of my favorites).

Bloom
$3.99
One of two Eno-based apps on my list. This music generation app is fun and addictive, plus it keeps the kids busy when you need some quiet in the car.

Darkslide
Free
A dedicated Flickr client that also uploads to your account directly from your iPhone.

Evernote
Free
Can’t say enough great things about this app. Just get it.

Fring
Free
Multiple protocol Instant Messenger AND Skype client. Yes, use Skype on your iPhone and tell AT&T to go to hell.

NetNewsWire
Free
Very good RSS client. Syncs with the desktop version also.

Now Playing
Free
Essential if you love movies like I do. Look up movies, showtimes, etc.

Oblique Strategies
Free
Brian Eno’s mystical fortune cookies for creative thinking

Twitterific
Free
People will argue about which Twitter client is better, I think this one is pretty nifty.