5 Twitter stars you've never heard of

(CNN) -- Sure, everyone knows that Oprah, Shaq and Ashton Kutcher are huge on Twitter. They're famous -- they should be huge on Twitter.
But Heather Armstrong? John Dickerson? Adventure Girl? These people can stroll unmolested through a paparazzi convention, and yet each has more than 1.2 million Twitter followers -- enough to rank them in the top 200 overall and more than Stephen Colbert, Snoop Dogg or Paris Hilton.