Bartosz Ptaszynski's dashboard

It isn't twitter, but it is a fully integrated Second Life blogging solution. http://www.SecondBlogger.com - check it out for details. You can post from in-world using the snap shot functionality and emailing as a post card, or log in through the web site to use the familiar Wordpress interface. It is free, and everyone gets a custom URL (such as http://flipperpaperegrine.secondblogg... - by avatar name).

twitterbox NCI has it in thier freebie area i have it on an alt works ok I also run twhirl on my desktop

Also have a look at http://sl-messenger.com/