i suggest taking it slow and downloading an app and using it. if you don't like it or don't think you will use it. get rid of it. also i suggest handcent sms, google voice, SMS popup, spare parts, and last.fm. i also have connectbot, wptogo, twidroid, transdroid, shopsavvy and Gdocs installed.
I say download everything you think you might like, try them all and delete what you don't want. Shopsavy is great if you have ever been shopping it is one of the two biggest reasons I got my android phone the other is sharing calendars with my wife. The program advanced task manager is good to help uninstall quickly too.
Here is my list so far.
Keeper for passwords
Samba Explorer to get files from your home computer via wireless
AndroZip for file browsing and zip files
PhoneFlicks for Netflix
K-9 email if you want to be able to change your reply address
Banking apps like BofA
Gem Miner game
Power Manager to help save battery
Speed Test to see what kind of network speeds you get wireless/EV
Bluetooth file transfer
Spare parts for more settings - all volumes
Ringtone scheduler so your emails all night won't keep waking you up
MyBackup to backup to SD card
Call Location so you don't have to guess 100% on area codes
Handcent SMS because it has a popup so you don't miss messages
Mortgage and car loan calculators
Scan2PDF is useful
Shazam is neat
Thinking Space for mind maps
If you find better let me know. I would really REALLY like an app to allow snoozing individual calendar events.
I really like Toggle Settings. I like the fact of being able to schedule my phone to go into vibrate mode while I'm at work, go into ring mode while at home, and go into Internet mode with the wifi activated while at home. It also gives you tabs that have quick toggle options such as turning wifi on and off very quickly. In addition it gives you a Task Manager (so you can kill NFL mobile since it seems to hog the battery).
The Weather Widget donate version is pretty cool.
Flixster is a good theater/movie app.
Zedge is an awesome wallpaper/ringtone app.
Shopsavvy and barcode scanner are very useful for shopping.