ManageFlitter. It's not bad and seems to be pretty accurate. It tells you how many people you follow don't follow you back, those who lack a profile image, inactive, talkative (more than 5 tweets a day), quiet, all followers and you can do a biography search as well. It also tells you how many people have stopped following you using the service.
Howl lets you post links to places like Twitter and Facebook and collate information about the link all in one place. You can do this with Delicious of course, but this looks quite neat. My link blog is here: philbradley's link blog Although to be fair I've not added anything, as I kinda have one already!
GlowDart. It's a streaming service - decide what resources you're interested in and it'll just stream a flood of data at you. Great for second monitors etc. Can log in with Facebook or Twitter, but can't see how you can turn this into a proper Twitter fountain, as you don't seem to be able to search - just choose streams. Available are Youtube, Hulu, Twitter, CNN, BBC, Google news etc, so a fair view + some others as well.
Have your Twitter followers already seen a link you're about to tweet? Link
different is an app that tells you. Allow it access to your Twitter account, find a URL you want to tweet and click on the bookmarklet. You'll then see how many have heard about it from someone else.
There's no indication as to how they know of it - if they may have read of it in their stream, or if they actively have to have tweeted or RT'd it, which would be useful. However, it's interesting, except for the approx. 10% of my followers who already know of it.
What is Buzzduit.com?. This is a microblogging platform that's not reached beta yet. Looks like an emphasis on twitter type lists with the added ability to post to specific lists, and search them as well. Nice idea, one twitter may well nick. Not sure where it would leave this one then!