The obvious free agent for me is Kerry Rhodes. The weakest link on this team is strong safety. Rhodes is arguably the best option at that position, but the coaches seem to be fairly high on Shawn Williams.
I had another thought: What about Desmond Bishop? The Packers appear to be shopping him. Possibly trade a 4th or 5th round pick for him? He appears to be an improvement at middle linebacker. There are a couple of question marks, though. He plays in a 3-4 defense and is a free agent after this season.
What about Brandon Lloyd? A good #2 wr? I'd personally stick with the wr's we already have. Anyways, who would you want of the available players out there?