It is my belief that you don't look for game breakers among free agents, if one comes available he is usually over priced and on the downside of a career. I think you look for good rotation guys, and good intangibles in Free Agency.
With that in mind along with the fact that Rome wasn't built in a day (so neither will the Broncos be rebuilt), these are my top free agents for Denver to pursue this offseason. (I used football's future to look up whether someone was a 2011 FA, so if contract situations have changed I apologize.)
1) Cullen Jenkins DE - If you have read my posts before you know that I think Patrick Peterson should be our top draft choice, so if there is anyone worth getting in a bidding war over it is the best Defensive Lineman out there. Jenkins is a great pass rusher with the girth to shift inside on passing downs. He is stout against the run and the Packers have multiple options for their 3 man front with Raji's continued development. I don't think the Pack resigns him or uses a franchise tag, that would represent a lot of money devoted to a single position that the Packers can't afford making him available. With Fox using nothing but coach speak on the subject of switching back to a 4-3, Jenkin's versatility to play multiple line positions (all but the NT really) would make him that much more valuable to the Broncos.
2) Matt Light OT - Yes, he's turning 33. Yes, he had his worst season this year. Yes, he's another Patriot (soon to be) cast off. Why do I like him. He played LT last year and we would line him up on the right side. As a Pat he was consistently better in the running game than the passing game. He is a great leader that our young line can look up to with some rings to help his credibility. I thought at many times that our line looked disorganized this year (that'll happen with 2 rookie starters), he would be a great locker room guy.
3) Barrett Ruud MLB - Another older vet, but I think he's got 2-3 good years in him. The Bucs almost showed him the door last year before camps opened. Great tackler and really good against the run. Personally I think he's best suited to an interior backer spot in a 3-4 given his speed and coverage limitations, but any run help would be good for the Broncos D. I do stipulate this with I think his starting days are behind him, and if he demands a starting position he should not be pursued (assuming we are switching to a 4-3 base.
4) Atari Bigby SS - Another one of Green Bay's many FA defensive players. This one has the dreaded 'oft injured' label, but I think he'd be worth taking a risk on (he doesn't quite have Bob Sanders reputation). He's a big hitter and the Packers don't need him. He could come cheap, and if he loses the injury problem could be part of what brings a hard-hitting reputation to the Broncos. His signing would spell the end for Dawkins in Denver, and probably indicate that Bruton is a special teamer for life.
5) Mike Bell RB - I know the popular sentiment is to get D-Will. Too expensive guys. Mike Bell is a former Bronco and a solid between the tackles runner, and would spell Moreno nicely. He also has the strength to spend some snaps at FB. I'm not sure why he wasn't pursued by the Broncos last offseason.