I think Snowe, Lincoln would both have a chance in the General, although I doubt with the direction the GOP is moving that Snowe would have a snowflakes chance in hell of getting the GOP nod.
She's not a senator, but what about Gov. Kathleen Sebelius of Kansas. She's a Bayh/Warner style Democrat which should be the kind we nominate, a southerner, and relatively popular.
A woman who is a moderate governor has the best chance of being elected President. Granholm can't run because she was born in Canada, so that leave Sebilius (as well as Napolitano from Arizona). Let's see how her record is as governor, and whether she has presdential ambitions.
I'd love to see the Democrats run Barbara Boxer. She's my favorite female Democratic senator (other than Madame Hildebeast Clinton, of course).