Reqwireless' WEbviewer. find eOffice, great demo of it, worth the price if you can afford to drop the money at one time for it, or email them to work out payment options as I have ;). That info is in another thread here.
That's all I got on mine at the moment other then some games and fun stuff to do when I'm bored
I am a big fan of beinbg able to view pictures on the BB -- you can either go to Terratial.com and pay them for one of their viewers, or if you feel up to the challenge, look for Klaus's open source Image Viewer application on the Java developers site at Blackberry.com. It requires you to get your fingers a bit dirty, but for no cost you can put a slide show of your favorite pictures on the Blackberry.
I find myself spending a lot of time playing Goro -- a version of reversi that I downloaded off of Rimroad.
Magmic has a bunch of really nice games -- Cribbage is very well done.
Reqwireless mailviewer or hotviewer gives you the ability to view graphic attachements to email messages.
If you are on BES, Webmessenger is great! I hate having to pay an annual license, but it is a great IM client.