From John Kremer, Book Market, here are just some of his twitter suggestions:
Google Twitter Gadget: Allows you to read and update Twitters right on your desktop.
Loud Twitter: This batch-tweeting service allows users to set up automatic posting of their tweets to their blog (a listing of tweets once per day).
Mr. Tweet: Helps you build meaningful relationships on Twitter, showing you the followers and influencers you should follow. Also recommends you to enthusiastic users relevant to you.
A free service that allows you to customize your Twitter page. Again, a customized page is a boon for helping you to brand yourself on Twitter. I (www.bookmarket.com) used this service to produce my current Twitter background in five minutes.
Ping Vine: A free service that takes an Atom or RSS feed from your blog, lifestream or favorite website and posts it to Twitter, Ping.fm or Identi.ca. Hence, you can automatically post your blog posts to Twitter via RSS feed.