When you first sign up for Twitter, you might feel a bit overwhelmed. Who should you follow?
That depends on what you're interested in.
The obvious first choice, is to follow people you already know. You know me. You know Delphiforums. Check out our friends. See anyone interesting? Go to their page, and check out their friends.
Don't follow everyone you see, but do follow people that seem to have something interesting to say. Follow people that you already have in your address book. Twitter will search through it for you to find your friends and forummates.
Use Twitter's suggestion page to find some prominent Twitterers.
Just because someone's famous, doesn't mean you'll like what they have to say. Be descriminating, and never be afraid to unfollow someone if they bore you, or even if you decide they simply tweet too much.
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."