Docs to Go (if you have OS 4.5 - Doc, Excel, Powerpoint files)
GridMagic (Excel editor)
Opera Mini 4 (alternative browser for sites that have trouble being viewed with the Blackberry browser - must have)
LaunchPads (shortcut to programs and apps - must have)
Google mobile app (access to Google Applications: Gmail, Maps, News, Reader, Calendar, Docs, Photos, Sync, Notebook)
GMail Mobile App (access to GMail accounts - must have)
Windows Live Search Mobile (maps, directions, traffic, movies, web search, weather)
BBSmart Alarms Pro (create mutiple alarms)
PeeKaWho (notified of incoming Email & SMS messages by pop-up window. Giving you the ability to read, mark as read, or delete the Email or message)
Google Maps (maps and directions with satellite and street view)
Crackberry App store laucher (shortcut to applications from Crackberry.com)
Superpages Mobile (Business & people search, movie & theater search, maps & directions, WiFi search, ability to save searches as Favorites)
Beyond411 Search (Yellow pages & white pages serach, Weather, shopping, movies, sports, local info search)
VZ Navigator (if you have VZW - turn by turn GPS voice navigation)
GeoTipApp (tip calculator)
BBNotepad (text viewer and editor)
RepliGo Reader (native PDF viewer)
BeamReader (native PDF viewer)
PaderSyncFTP (upload and download files to your personal web page account)
ShrinkIt! (resize pictures to a smaller size taken with your blackberry camera, making it easier to Email pictures. It keeps a backup of the original file)
Personally, I always IM n I love the Beejive application ($20-$30) on my BlackBerry. Great part is it works over WiFi, so if you don't have a data plan, I can still have unlimited IMs I also love the Live Search app!
Posted from my CrackBerry at wapforums.crackberry.com