I suspect, as do others writing on this topic, that a President-elect Obama would go out of his way to pick a few high-profile Republicans to place in his cabinet. If I were a gambling man and had money to burn, here would be my picks for two of the most important cabinet posts.
Secretary of Defense
Colin Powell. It is doubtful that Obama or Powell would want Powell to take another turn at State. Given his years of military service and the difficult situation the U.S. military is in right now, Powell would be a smart choice.
Another possibility is that Obama would ask Robert Gates to stay on for a year or two. Gates is well-respected on both sides of the aisle. What better way to calm the fears of the defense establishment than to continue with the sitting Defense Secretary?
Secretary of State
Richard Lugar (R-IN). Perhaps the most respected foreign policy mind in the U.S. Senate. Could Obama convince Lugar to give up his seat on Foreign Relations as ranking member? Probably. He would be a great fit.
Another possibility: Senator Chuck Hagel (R-NE). Hagel and Obama get along well and Hagel's wife publicly supports Obama (Hagel won't tell who he's voting for--which means he's an Obama guy). A Vietnam vet who has never been shy about speaking his mind on the Iraq War, he would also be a smart pick.