WhoTheTweet analyzes the most recent tweets from a username you type in and gives you back a tag cloud, of sorts, about their topics. This gives you a quick view into whether you should follow someone or not.
They show the last lookups across the bottom of the homepage and then there is a few places for premium tweeters, but you have to buy a slot to get on there. Monetization ideas are everywhere I see. I ran my name as usual and it took about a minute to get the results. But they were right on and looked good to me.