Well I use many apps on my BlackBerry and demo more apps than I could count, but I do have some apps that I would not be without. Here they are.
UberTwitter: Free Twitter Client with many included features. DOWNLOAD HERE. .
RestartMe: Simulates a Battery Pull. Very handy Applicaiton. DOWNLOAD HERE.
Captureit: Take a picture of what is on your BlackBerry Screen. DOWNLOAD HERE.
Google Mobile App: Access several apps in one. DOWNLOAD HERE.
SmartBBattery: Shows battery status as application icon on device home screen. DOWNLOAD HERE.
YourShortcut.mobi: Mobile Site Portal Launcher OTA DOWNLOAD HERE!
BlackBerrySites.com: Launcher for your Home Screen. OTA DOWNLOAD HERE!
Super Store: Four stores in one with dedicated showcases for BlackBerry apps, games, themes, and accessories. The applications and accessories that appear in the store are filtered to ensure compatibility with your specific BlackBerry. And all the software products featured in the Superstore are downloaded easily over-the-air (OTA).Tons of Free Stuff also. OTA DOWNLOAD HERE!