The Republican primary has looked like a steeplechase for three legged horses - lots of tripping, falling, and hilarious attempts to get over every hurdle.
Mitt Romney (1 to 1)
Mittens is trying to prove he can buy an election where most people voting despise him. His financial and organizational advantages are huge (he's 1 to 3 on Intrade) but not decisive. Romney will win the West (Mormons) and Northeast but get his clock cleaned in the Mid-West, South, and Bible Belt.
Rick Santorum (5 to 1)
Frothy's strength is he is Flavor of the Month (I'm sorry, that's disgusting) while there is actual voting. His weakness is he's not even on the ballot in Virginia and Indiana and doesn't have a full slate of delegates available in several other states.
Brokered (6 to 1)
Jeb Bush, Chris Christie, Sarah Palin, Mitch Daniels. There is a far dinkum chance that the end of primary season will see Romney with a majority but not plurality and unable to negotiate a surrender by one of the others. A Republican brokered convention will be an open auction with millions being spent to buy delegates.
Ron Paul (10 to 1)
Don't underestimate the mole rat. Most of what he does is underground, procuring delegates by stealth. If the convention goes to multiple ballots he might unleash a flood of hidden Paulbots and steal the nomination.
Newt Gingrich (30 to 1)
The zombie salamander has regional strength in the Old South and nowhere else. Romney's biggest nightmare is if Gingrich and Santorum form an alliance and tag team Romney to death. In this scenario Newt should end up as the Veep candidate but their roles might reverse.