1. Tweetdeck (Twitter)
2. i.TV (awesome tv guide)
3. SMSenger (free text messaging)
4. Flickr (quick way to upload photos to my Flickr a/c)
5. MeeHive (picks up news that I don't see anywhere else and topics can be customized)
Skype -- how well does it work on 3G?
Navigon -- too slow. Tom Tom is much much faster.
AccuWeather -- better than WeatherChannel Max?
Here's some serious apps:
1password - stores all private info (banks, serial numbers, passwords etc) and syncs with OSX.
Analytics App - Avoids using Mobile Safari to look at your Google Analytics stats.
GoodReader - can open massive pdf files (good for manuals)
FlightTrackPro - great for checking flight information and status (when a flight will be late etc)
PdaNet - (free tethering when you visit someplace that doesn't have WiFi)
Shazam - toy but useful!
Skype - No 3G for the moment, but It works fine with WiFi besides all your friends already have a skype account.
Navigon - Maybe a bit slower but supports more countries and has everything you need.
Accuweather - far better, supports more locations, indicates your position everywhere.