Some of the applications I like are Google Maps. This allows you to search for businesses based on your location, and they show up on the map. And it is great because the Curve 8900 has built-in GPS.
I also like PageOnce, an application that lets you set up different accounts and view them all in one application. I have my credit card accounts, banking account, cable, cell phone and student loan account all set up. They are updated periodically so I can see all accounts quickly.