HootSuite
HootSuite is a REALLY comprehensive tool - it does a lot more than I need, or than most people need, but it lets you use multiple Twitter accounts and manage them all from one dashboard, track your statistics...you should check it out for yourself...it's free right now, but it's the type of thing they'll probably start charging for, but if you set up an account now you might be grandfathered in!

Tweepular
This is another fairly comprehensive tool, it makes it really easy to manage who is following you and who you're following. Everyone jokes about the color scheme, it's pretty over the top, but I like it!

Tweetlater
This is probably my favorite. Again, handles multiple accounts through 1 login, then allows you to schedule automated replies for new followers, allows you to auto-follow people who follow you. Not as pretty as Tweeplular, but good.

There was a lot of buzz about this as I was researching stuff, but frankly I don't really like it that much, it seems to have a LOT of cool features available if you UPGRADE (and pay $) but I'm not really interested in paying for what I can get free!

FutureTweets
This is cool because you can schedule Tweets around specific events like your friends' birthdays, or Holidays etc. Easy to set up, it's got some other fun things to play with too.

TweetBeep
This is just like Google Alerts for Twitter. It could get overwhelming though because people Tweet so much, but you can select search terms or your name or whatever you're interested in - also gives you the opportunity to keep track of people tweeting on certain topics or about you etc. etc.

So that's what I've seen for managing Twitter combining these tools can put your twitter on autopilot adding value for your followers, building followers, and extending your network - what tools have you seen? Leave comments below!