HelloTxt enables you to update your status across all of your social networks and microblogs with a single click. (Currently supports Twitter, Jaiku, Pownce, Facebook, MySpace, and Bebo.)
Many forums, Blogs, and other web services allow you to have images as part of your signature. twitsig.com allows you to display your current twitter status as an image. [via cygnoir]
Alex King's super-duper plugin that completely integrates WordPress and Twitter.
Twittering the first lines of books so you don't have to. (Admits to being an Amazon affiliate.)