Formatting for clarity:
Sen. Allen - the front-runner
Sen. Brownback - Probably running for VP
Sen. Thune - His name has been thrown around as a serious "sleeper" candidate in 2008
Gov. Pawlenty - Popular Conservative Gov. could give the GOP the great lakes states
Gov. Sanford Gov. Bush (won't run)
Gov. Owens (if marriage is fixed)
Newt Gingrich
I thought I heard that Mark Sanford has taken himself out of the running for the '08 nomination. If so, its a pity. I've been watching his career for several years now and I am very impressed.