While this is very open to debate, I would suggest that 2 of the best APPS available for any BB are:
BerryBuzz
QuickLaunch
You can choose your own weather app, gps app, and anything else you'd like later. These 2, in my opinion, are such great APPS that you would think they are a native part of the system.
BerryBuzz extends your default Blackberry alert system. BerryBuzz allows you to customize the LED color and create repeating audible reminders for many alert types.
It will repeat alerts until acknowledged so you will never miss an alert again.
Must have is quicklaunch
Opera 4.2 for quick browsing
For planning and organising thoughts or ideas Mindberry is great
My top app though is todomatrix, but you pay a lot for it
Posted from my CrackBerry at wapforums.crackberry.com