I nominate Jim Demint or someone like him.
Jim DeMint is where he wants to be, and where he is most needed. He's also said repeatedly that he is NOT running for president in 2012.
He also doesn't have a huge groundswell of support for a run at the White House, such as Sarah Palin does.
Having a sterling conservative record and being on the right side of the issues, is only a part of the total package. DeMint would have to show some fairly strong leadership qualities for most Americans to consider voting for him. It's hard to demonstrate that from within the marble halls of the US Senate.
Some Democrat presidents have risen to the office of president from the Legislative Branch, but it's rare for Republican presidents to come from there. Abe Lincoln is the only one I can think of, offhand. Republican voters normally prefer to vote for ex-Governors or Vice Presidents. Ike was an ex-General of the Army, but that was also an executive position.
DeMint would have to break new ground in that area alone, to be elected.