I read a recent mention of Wesley Clark; it seems like a Dean / Clark ticket (Google turned up an interesting discussion from back in January) would make a lot of sense.
From a great post by Matt McIrvin:
This election, if lost, won’t be on the nuances of the issues anyway, it will be lost because of the more electoral efficient disbursement of GOP voters, a more enthused and loyal GOP electorate, and a GOP that will have $200 million dollars to craft its message. The 2002 midterm elections as a guide, show that in close races the swing voter did not perceive a difference on the issues between the Democrat or Republican and/or they did not know what the Democratic position was. There needs to be a very clearly articulated difference. Everyone knows what the GOP stands for Tax Cuts and Defense Spending. People are fuzzy on what the Democrats stand for, I think Fiscal Responsibility and Civil Liberty is a good start.