Skyfire browser - Enables you to watch flash videos AWESOME.
DocsToGo - You can create/edit Word, Excel or Powerpoint documents and use them on your home computer.
IMDB - If you're a movie buff
Netflix Mobile - If you are a subscriber
Garmin StreetPilot - If you don't have a GPS, it's only $40 and FREE UPDATES!
Angry Birds - I know, it's the most cliche game, but it's the top selling app for a reason, addicting!
Hipstamatic - Amazing photography app with different filters and such. Camera + is cool too
iHeartRadio - Listen to all your local and national radio stations.
Red Laser - Scan items' barcodes and find discounts at local stores and such
WhitePages - Awesome reverse phone lookup, so you can find out numbers you dont know
TheWeatherChannel - The current weather app sucks, but with iOS 5 coming soon, you won't need TheWeatherChannel anymore, so definitely dont buy the ad-free $5 one. Get the free one.
Shazam - Listens to a song and tells you the artist, song name, album etc.
Well, that's about all I have for now. I have 1000s of apps, but only about 50 currently installed. I'll let you know if i figure out more you'll like.