McCaskill?

Cross her off the list:

Obama hangs out in StL without me: "While lauding her as 'such a terrific advocate on my behalf,' Obama sought to tamp down any speculation that McCaskill — a first-term senator like himself — might be chosen as his running mate or for a possible Cabinet post if he's elected.

'My sense is that Claire really enjoys being the senator of Missouri. We haven't had any discussion about other roles,' Obama said."

That seems pretty definitive to me. If he were seriously considering her, he would have at least said "maybe" when in her home town.

Fun Fact: One of my many right-wing uncles is a Priest, and McCaskill belongs to his parish.