My best guesses are Charlie Crist, JC Watts, Lindsey Graham, or Mark Sanford and my long shot would be Joe Liberman, THAT choice would light a fire in the tinderbox. But he really can't afford another "moderate" on the ticket with him. I've also heard Phil Gramm, Mel Martinez and Jeb Bush mentioned. I doubt they will get a serious look though.
My preference would be Sanford, Crist, or Watts. Any of the three would make a fine President.
EDIT: Ah I see, yeah, running mates. Sorry.