Here are a few of the twitter tools I use the most.
For the Blackberry I have been using Twitterberry. The current version is .08. I just upgraded to it from version .06. Using the blackberry browser to twitter is slow. This app gives you a direct connection for updates.
For finding who to follow, I use Mrtweet. They show you why you should be following people following you, and who the people you follow are following. Is everybody following that?