One of the native applications I use regularly on my BlackBerry (multiple times per day) that I've noticed for some reason many BlackBerry users either do not use or don't even know it exists is the BlackBerry Password Keeper. On newer devices you can find it by default within the Applications folder on the homescreen ribbon.
The BlackBerry Password Keeper is extremely handy and does exactly what you would think it would do... it provides a centralized location where you can store critical account information. You create one super duper master password for the BlackBerry Password Keeper and from there within the Password Keeper client you can add multiple accounts containing account/login information for the various sites/services you frequent. Be sure to watch the video for full details.
Soooo many people in this world still either use one password for every account they have or different really, really crappy passwords (something1234 anybody??). The BlackBerry Password Keeper features a Random Password generator which makes it easy to come up with crazy passwords. And since the BlackBerry is remembering the passwords instead of your brain, you can make each different account you use feature a different crazy password. All in all, I'd say it's a good thing.