My two favorite apps are QuickLaunch for shortcuts and a host of functions it includes, and now, Fixmo Extend to tether my laptop while I'm on the road.
These are the ones I've installed and use regularly:
Whatsapp
Facebook
Quicklaunch
Quickweather
Poynt
Scoremobile
Gist
Stocks+
Wikitude
Localipedia
Gasbuddy
Google Maps
Crackberry
Facebook
Social Feeds
Google Maps
Flixter
Bebuzz
WiFi Manger (auto-disables WiFi when not in range of configured accounts to save batt life)
BlackBerry Travel
BlackBerry Bridge (if you have a PB)