Viira is one of the more evolved Getting Things Done (GTD) app for BlackBerry and it has just been updated to version 2.0. This new version integrates into the email system letting you create and classify tasks based on email. It is a GTD way of managing your inbox.
The app also integrates with your calendar and lets you organize your appointments by project, context, and more. It even lets you use the volume up and down keys to toggle between the organization/sorting options.
You can find more info about Viira at www.kartamobile.com. The app is a pricey at $29.99 or $19.99 for an upgrade but they do have a free trial.