A list of some useful tools for managing your twitter accounts.
they have been divided into two categories:
1) follower management
2) analytics

1) follower management
wefollow.com – fill in your details so that others can follow you
untweeps.com can use 3 times a month to unfollow stale peoples
tweepi.com – loads of things: find cool people to follow.
twitblock.org – scan twitter following for spammers so you can remove them

2) analytics
http://tweetlevel.edelman.com/ – sort of test suite to see how good you are on twitter.
twitalyzer.com – stats about your twitter account!
http://stats.brandtweet.com/ – stats, unfollow, etc
twittercounter.com gives some insight to follower stats. very useful and free =)
hootsuite – gives you some stats on retweets, etc
raven tools – impressive pro level analytics for twitter
ubervu – impressive pro level analytics for your social media campaigns. not free.

everythingtwitter.com – awesome site that has lots of tools to help you make twitter lists, etc.