Comtwit - posting to Twitter from the command line
TweetPeek - create a Twitter stream from a selection of users, basically a group Twitter feed. You get your own URL people can visit to see the latest tweets from a bunch of people. There is also a page listing the contributors, RSS, and a widget.
TweetBurner - A Twitter URL shortner that also enables you to post the tweet on one-click. The page tracks most popular tweets using this service.