I have tried Tiny Twitter, Twitterberry, Twibble, Blackbird, Tweetcaster, Tweeteev, UberTwitter, and another I can't remember the name of. Even with the ads, UberTwitter is the best. I am still waiting for an invite to SocialScope (since July) but I am not holding my breath.
Posted from my CrackBerry at wapforums.crackberry.com