Twitter Extras

Tweetcloud another web service based on twitter which can reveal far to much about you.

Another twitter 'add-on' I have seen recently, but yet to test out is TwitterLocal.

Update:
Just a couple of others:
Twubble - Searches for your friends friends - to help expand your network.
Twits Like Me - Another one to expand your network, searches for people with similar text in their tweets.