I'm going to be different and say Dino Rossi. Well, if he manages to beat Gregoire that is. If not then forget about him.
Is Dino a first tier brain? Does he have the right stuff for the major leagues? Just asking.
I don't know. Gregoire's campaigns have been pretty awful. Still, WA Governor is the only possible major pick-up (Governor and Senator) the Republicans could have this year. If Rossi wins I fail to see how he won't be noticed because of this.
I'll also say he's good at appealing to formerly Republican suburbs that have been trending Democrat recently, while still making far right-wingers happy. The Republicans already don't have a chance in the cities, and if McCain loses a lot of traditionally Republican suburbs to Obama, this will be another factor the GOP will want to consider.