Tweetake - get an excel file back up of your tweets, followers, people you follow or all of it.
FLOATwitter - the icons of the people you follow on Twitter are all floating around, hover over them to see the latest tweet
ToAnswer - Q&A on Twitter…follow both the Twiter users “ToAsk”, “ToAnswer”
eg. @ToAsk Are there any good pizza joints in downtown Los Angeles?
eg. @ToAnswer [question id] No, there’s no such thing as good pizza outside of NYC.
A similar service is AnswerMe.