I think it will be someone who meets these criteria:
1. Must have national stature;
2. Must be a political moderate or conservative democrat;
3. Preferably from the South or Midwest;
4. Younger than Kerry and more dynamic (that means anyone under 50 will do);
5. No major political downside, e.g. Joe Lieberman would have with the anti-war wing of the party.
These criteria suggest Edwards as the strongest possible candidate. I love Feinstein, but the Dems will carry Cali so why pick her?
Also, picking Edwards will almost guarantee the red-neck waitress vote.
-Robert