KeePass has been around for quite awhile allowing you to store passwords with secure encryption. They have just released an unofficial client for BlackBerry devices that allows you to syncronize your password protected information with your BlackBerry device. The best part is that it is completely free. Personally I use MagicSafe but that is a commercial solution and does not have as many features as KeePass. Another nice part about KeePass is that it has a USB stick version of the software so you can run that off the mass storage mode of your BlackBerry or USB stick.
Check out the KeePass website here:
And the BlackBerry Client project here:
Thanks Josep for the tip!