The only one that I'm definitely sure would do it in a heartbeat would be Joe Rogan.
The way around getting more celebrities would be more of a paparazzi/viral method.
For example, say you live in Los Angeles. You and a friend are walking around &
see Drew Carey standing in front of a local coffee shop or or John Mayer waiting
for the valet to get his car. You ask for a photo & your friend instead videos with
his iPhone while you ask him what he thinks of Ron Paul. If it's super positive, post
the video on Youtube & then link the video on Reddit, Digg, etc. It would be a lot
cheaper than traditional commercials.