ilo - Premium Twitter analytics
BlockParty - Real-time voice chat rooms from the creators of turntable.fm
Accountanalysis - A tool to evaluate Twitter accounts
Secateur - Use Secateur if you want to temporarily or permanently block or mute (or both block and mute) a Twitter account and all its followers.
Tweetastic - Better Twitter analytics, scheduling and more
Twitter One Click Block - Add a block button for a simple one click blocking.