Twitalyzer

What can I say about Twitalyzer? It's an amazing site.  You can find out your Twitter impact or the impact of your favorite users.  Your clout, lists, followers, followings, signal, generosity, velocity, engagement, influence and impact are all analyzed.  For a complete list of how they score a user, along with an explanation, click here.  Plus, they have a discount program for nonprofits if you want to use one of their paid plans.  The average user doesn't need a paid plan though.