I'll start with some free ones, as I haven't ventured into Rooting and what not cuz I keep having to warranty my phone every month.
Apps:
aCar--Not bad, keeps record of your car's services and what not...gives you reminders
Album Art Grabber-Works GREAT in conjunction with Music Wizard. Does as it says.
Bump-Great Bluetooth connection tool to share files and apps
Battery Status-Gives you an actual # of % battery life left, goes Green/Yellow/Red depending on % left.
Dictionary.com-Do I need to write a description?
Ebay-Ebay App...ok.
FourSquare-If you 4Square you know what it is, if not, you log into places and it connects with your FB and posts a nofitcation and you can send it to friends as well.
Google Goggles-They're Fun, scan shit with the camera and google identfies it and finds it.
Instant HeartRate--Actually works, not entirely accurate, but fun and close
Key Ring-Ever goto the store and not have your stop and shop discount card thing on you? Great, Scan the barcode with your phone and it is saved and you can display it on your screen so the cashier can scan it.
Mob Decor Wallpaper-Finds really really good looking wall papers, cars, girls, etc.
Music Wizard--Free music. Find the song you like, type it in the search. Music wizard gives you a download of the song for free, full song, no albumb art.
Mp3 Download- Same as above, just uses different search engines.
Photobucket- Mobile photobucket App, very useful for me anyhow.
Retro Camera- Great Camera app for taking old style pictures, has 4 different camera types to choose from.
Scanner Radio- Listen to Cop/EMS/Fire radios in your area
Speed Test-Currently how fast your download/upload rate is where you are.
Super Security--Anti Virus, there are tons, I like this one. Comes with a "I lost my phone" option. You can text a # to your phone and it locks it for you until you enter in the security code...making your phone worthless and displays a pre-set message you put.
Tikl-Touch to Talk, basically Nextel for andriod, only works if someone else has program and they have it launched at some point so its running in background.
Where-Finds shit for you- Gas, food, etc.