Carl is looking for a stay busy / tick over fight until the Bute rematch, he was looking at Kessler rematch but it seems Kessler is demanding silly money for some reason. Options I have heard being mentioned are Thomas Oousthausen, Kelly Pavlik and Sakio Bika, all of those guys fit the Bill for a Froch fight in my opinion, it's just a case of which one.
Myself i'd like the Oousthausen fight, he brings the IBO title (minor, but still a belt), a top 5 ring ranking and undefeated record, plus he's got a following in South Africa and I think he'd bring a few fans over with him.
Pavlik would be second choice, although I don't belive him to have much left in the tank, and I think his "name value" is being overrated in business terms, I don't feel he'd provide much of a cash injection to a Nottingham fight, he would also probably ask for silly money.
Bika is third choice, he just doesn't bring much except a hard nights work, and an ugly mess of a fight.