As pointed out by verno329, Mike Florio says that Favre is giving on returning to the NFL, for now. We shall see.

Peter King looked at who has salary cap space available and decided Tampa Bay makes the most sense:

Tampa Bay. Mark my words, people: The Bucs are going to be heard from in this story if the Packers decide to move him or let him walk. They most definitely will be heard from.

Aaron Schatz thinks that Baltimore makes the most sense:

I wrote about this a week ago, but I think the only team that makes sense is Baltimore. The Packers will never allow him to go to a team in their division, and I can't see them trading him within the conference either. Baltimore is the one team in the AFC with a clear hole at quarterback, a championship-caliber defense, and the ability to take on a veteran with one or two more years left because they have a young franchise quarterback waiting in the wings.

They don't have enough cap room for his $12 million base salary, but I would be stunned if he wouldn't take less money for the opportunity to play, and start, again.