Whoops. Barrow's out. Most likely candidates are Jason Carter, Michelle Nunn, and Scott Holcomb. They have a small chance at winning if Broun or Gingrey win, but this seat now Leans R.
Actually, check out this survey. Nunn seems to have pretty good numbers here.
I heard (this was right when Barrow opted out). I'm taking this with a grain of salt. It may have been only 2 off of the Barrow race and the presidential election, but this is Georgia that we're talking about. Plus Michelle Nunn isn't exactly a Blue Dog either.