Another way to find famous people and/or influential or popular twitterers (aka tweeps by some people, but that's a little too jargony for me) is to check this site:

http://wefollow.com/

Still trying to figure out who to follow? You can sign up for Mr. Tweet, and give (and get) recommendations of Twitterers of interest. Their main page says they're for "Helping you find great people and followers relevant to your interests."

This app says, "Get the most out of Twitter by finding the right people to share the conversation: Tweeter Tags makes it easy to declare your interests and find new, like-minded friends. Have a question you need answering? Find relevant people on Twitter to ask. It only takes a moment to sign up and tag yourself."

If you're tweeting for or to a very specific group of people or interests, might be well worth signing up for. I can see using this if you had a knitting forum, a horse forum, a Mac forum, or any other kind of specialty forum.

Tweeter Tags