There are over a dozen Twitter clients for BlackBerry and new ones are popping up all the time. The newest player to the Twitter game is TweetCaster by Handmark. It doesn't boast any revolutionary features, but it does get the job done. Multiple account support, URL shortening, GPS and trending topic list are just a few. The layout is a bit rough and needs some work, but the app is a good start. TweetCaster is free, and to get it all you need to do is head to this page and send a Tweet. You can also check out a demo video here.