I've tried dozens of ToDo applications on the Macintosh, Palm and Windows Mobile platforms, and ToDoMatrix is the first one that actually works for me. The interface is simple, it's always with me, and it's rock-solid in terms of reliability and support.

The integrated web version is continually synced with your device, and a separate backup keeps your data safe and makes it easy to migrate to a new BlackBerry.

REXWireless' website has a very helpful user forum with all kinds of experiences and suggestions from current users that help to get the most out of the application, and the REXguys have a great whitepaper outlining the various time-management methods that can be adapted for use with ToDoMatrix.

The only negative reviews I've seen are due to the price, but I've yet to read about someone who tried the demo and did not like it. It's really liberating to have a trusted system with you all the time that can hold everything you need to remember.