Broncos are in pretty good shape on the cap, they free 19 mill by cutting Peyton, so they can re-sign Miller easily.
Some free agents I think make sense are guys that might get cut because the team doesn't have the cap, not necessarily because they don't 
want the player.  You hear a lot that teams don't ever really let the guys they like get to free agency.  That's why there are so many big free agent busts.
But when a team has made some salary cap mistakes, and need to cut good players for cap space, that's when I think you can get a good free agent.
Looking at 
http://overthecap.com/salary-cap-space, you can look at which teams are up against it on teh cap next year, and easily see who might get chopped.
Miami:  Just a horrible Suh contract.  They might cut Brent Grimes, Jordan Cameron, Reshad Jones
Buffalo:  They will probably HAVE to cut Mario Willaims and Kyle Williams.  You could make an argument for both in OAK.
New Orleans:  They are screwed.  They might have to trade Brees.
Patriots:  Jerod Mayo is a goner.
Steelers:  I dunno, maybe Timmons.  They picked up DeCastro's option, will work a long term deal.
Redskins:  Even after they cut RG3, they might cut Goldson, Garcon, and even DeSean.