Something that would pull the tasks from gmail tasks into Blackberry's built in task manager and vice versa. I'm sure plenty of people would pay a few bucks for this - at least until Google releases their own version.
I know you can visit gmail.com/tasks but that is not a fun solution.
If you have quicklaunch you can set a shortcut to the gmail tasks site. That is what I did for google reader and it works great. That might not be the fun you are looking for though.
Posted from my CrackBerry at wapforums.crackberry.com