Cardigan is a simple web app that scans your Twitter history to identify tweets you might want to delete.

TwitWipe is a tool to wipe or delete all your tweets in one go. You may need to do this to start over, to clean it out before handing the account over to someone else, or maybe you've just realized how nonsensical your tweets are! Whatever the reason, TwitWipe is the answer! Don't delete your account and followers - just TwitWipe it!