Flaptor - like Tweetzi this is an alternative Twitter search
TwitterSplit - when you link to a site in a tweet, and people click on that link, the URL will be a domain of your choice (eg your blog), then a ?, and then the domain you are linking to http://yourdomain.com/anydirectory/anypage.html?http://www.external.com
Twi8r - in the spirit of 140it, you type in a tweet in regular english, and it will translate it into text message shorthand...it doesn't really do a good job if you ask me.
Less Friends - do the people you follow on Twitter follow you...also see FriendorFollow.
Twittley - a memedigger for Twitter. If you vote a link it will auto-tweet it on your profile. For similar memetrackers, see my post on microplaza.
BONUS
Birdsall's Massive Twitter Sites & Tools Directory