If you're a Twitter fan, you'll want to take a look at Social Rank. It's a very neat tool to slice and dice the followers that you've got. Simply log in with your Twitter credentials and start to have fun with all of the different filters.
You can sort by Most valuable, and in my case it's the British Library, followed by ReadWrite. I can check details on these followers by seeing who they follow, have as followers, the number of tweets they've put out, and their Klout score. You can also see their most used words and hashtags.
Alternatively, I can search via biography keyword - biographical details, names and handles. (want to find out how many of your followers have a podcast? This'll find it for you in a matter of seconds).
I can filter on words and hashtags, location, verified accounts, activities (as in recently tweeted, previously tweeted, never tweeted), company, number of followers they have. You can also compare accounts.
It's a nice easy and quick tool to use.