Check out this nice list of Twitter tools (and a few runner-ups) Peg Fitzpatrick lists on her website. The post, 5 Tools Everyone on Twitter Should Be Using, offers some apps for everything from finding the best time to send your tweets to tools for creating visuals which will likely draw more attention to your message.
I came across the link in one of Chris Snider’s weekly newsletters. If you haven’t subscribed to it, you should here. He shares some great tips and tools.