One of the most solid native apps to come out of the BlackBerry Beta Zone in recent memory is Twitter for BlackBerry. Twitter 2.0 brought with it many solid features and performance. RIM hopes to build on this with the release of Twitter for BlackBerry 2.1. Some of these features include:
Multiple account support
Last tweet sent no longer visible from Profile (which I personally can't stand)
If plans stay on track, Twitter for BlackBerry 2.1 will be releasing the Beta Zone some time next week.