Although a lot of Republicans say they were "Tea Party" before there was a Tea Party (yeah, we're talking about Rick Santorum), Texas Congressman Ron Paul probably fits that bill as well as anyone.
Paul is a full-fledged Libertarian of course, and ran under that party's nomination for president in 1988. But he drew the most press coverage of his long career with his iconoclastic run for the GOP nomination for president in 2007-2008.
He is set to announce in Iowa on Tuesday that he is forming an exploratory committee to run for the 2012 nomination. He announced this on Fox News' Hannity program, where Paul also got into a spirited exchange with Sean Hannity regarding Sharia law.