OperaMini
Face it; the BB Browser isn't too great. OperaMini makes your BlackBerry browsing nearly as good as what you get on your computer. Now, in version 4.1, there is BIS and WiFi support!
www.OperaMini.com

JiveTalk
Multiple IM clients in 1 app. It's free for 30 days and then a $20 1-off-fee. Well worth the money!
www.BeeJive.com

Google Maps Mobile with My Location
I prefer BB Maps myself but for those of you without GPS or for those whos GPS has been blocked, this is perfect. If you have GPS it uses that, otherwise it uses cell-tower triangulation to find out where you are.
maps.Google.com/gmm

Viigo Project Tango
Pre-release of Viigo's next release, Project Tango.
www.Viigo.com

DISCLAIMER:
- I CANNOT BE HELD RESPONSIBLE FOR DAMAGE TO YOUR BLACKBERRY CAUSED BY APPLICATIONS
- I CANNOT BE HELD RESPONSIBLE FOR THE CONTENT OF EXTERNAL WEBSITES