I am a BES admin so here are my top 5...little different than others.
1) Idokorro Mobile Admin - This is a superstar admin product! You can do Windows Administration from this tool on your BB. Life saver. More info go to Idokorro Mobile Admin
2) Viigo - I know others have stated this one but for someone on the go that likes to stay on top of the latest news for anything this is essential.
3) Google Maps - TeleNav - If you don't mind paying for a turn-by-turn GPS solution go with the TeleNav product...if your cheap and just want directions go with Google Maps.
4) Idokorro Mobile Desktop - This is a Remote Desktop session tool. I use this for connecting to my PC's in my environment to troubleshoot or doing functions on servers that I can't do with Mobile Admin (few and far between). Idokorro Mobile Desktop
5) Idokorro Citrix Client - This may be #1 on some of our Citrix people in our environment but we just started using this product. I saw it at WES this year and have a close relationship with Idokorro due to the other products (as if you couldn't tell!) so we were able to get a few licenses. This may change the world of users on a BB in the business world. Idokorro Mobile Citrix Client
Others that just missed the cut: Texas Holdem, Enterprise Messenger (Sametime IM client for a BB), Yahoo GO, Yahoo Msgr