What say you politicos about his running mate? ...
He's going to need a conservative Southerner I think (mainly because he's a moderate)...maybe Huckabee...or it may be one of his Gang of 14 friends like John Warner, Lindsey Graham, or, possibly, Joe Lieberman (which would make for an interesting campaign).
Colin Powell would be a strong choice as you suggest but I think he'll distance himself from anyone associated with the Bush Administration. Likewise, Huckabee aside, I will be very surprised if he picks any of his former competitors.
Something tells me he'll pick someone relatively unknown on the national political stage like Gov. Rick Perry of Texas for example.