Andrew Breitbart has offered a $100,000 to the United Negro College Fund for anyone who can prove Tea Party protesters hurled racial epithets at Rep. John Lewis and members of the Congressional Black Caucus during an anti-Obamacare rally in Washington March 20, 2010. You can see from this video the crowd was boisterous and noisy, but you don't hear any racial epithets. Apparently, the New Your Times can't find any evidence either. They are walking back the claim.
From Power Line:
..there is no evidence that epithets reportedly directed in March at Representative John Lewis, Democrat of Georgia, outside the Capitol, came from Tea Party members.
You can see a screen capture of correction at American Power.