Mario Williams (DE)
At 31 years old, Williams may not be one of the top pass rushers in the league anymore, but - as Denver showed with DeMarcus Ware - veteran pass rushers are still highly valuable, even if the stats don't light up the scoreboards like they used to. Super Mario has posted double-digit sacks in 5 of his 10 seasons in the NFL and has an impressive 96 total sacks over his career. At 6'6" and around 290 pounds, he's a beast of a man who can be a factor against the run as well. Just two years ago, Williams recorded 14.5 sacks with the Bills, so it's not as if he's completely washed up either. The bigger issue may be the money he'll be looking for, despite being over 30. The thought of him lining up opposite Beasley conjures images of a pass rush few Falcons fans would dare dream of. If the Bills do cut him, I pray that the Falcons are the first to pick up the phone.
Danny Trevathan (LB)
The Falcons desperately need an upgrade at middle linebacker, and Danny Trevathan fits the bill perfectly. He can play the run and he can cover, so he's not coming off the field in passing situations. Trevathan will be just 26 by the time the season rolls around and he's going to land himself a nice contract with a team looking for a young stalwart in the middle of a defense. Bring him home, Falcons.
Mario Williams (DE)
He's not technically a free agent yet, but it seems so inevitable that I'm going to go ahead and salivate over the possibility. Williams is on the wrong side of 30, but he's still one of the league's better pass rushers, his utter misuse in Rex Ryan's scheme in 2015 may have damaged his market value just enough that the Falcons would consider him, and he'd immediately become the team's best pass rusher and the ideal player to have opposite Vic Beasley on the defensive line. You may only get 2-3 quality years out of Williams at this point, but given how hard up for a pass rush Atlanta is, I have to think he'd be worth signing.
Von Miller (Hey, he hasn't signed anywhere yet)
...but seriously, Danny Trevathan (LB)
In an ideal world of free agency, you want players that are two things: 1) young and 2) good. The majority of the time, you either get a player that is one or the other, but Trevathan is not only both young AND good, it's highly likely he'll be leaving the team due to the amount of money Denver has to pay Von Miller and a quarterback. While Paul Worrilow is a fan favorite, it's clear he's not the answer at linebacker for the Falcons, and if they want to take the next step on defense, they need a guy who can come in and enforce the middle of the field. Trevathan should be able to do that.
Kelechi Osemele (G)
The interior of the Falcons offensive line is a mess right now. Bringing in Kelechi Osemele from Baltimore would shore up one of the guard spots. Osemele is a perfect fit for the Falcons current offensive personnel; he's athletic enough to run the outside zone concepts, but powerful enough to run the gap plays that better suit Tevin Coleman. He'll turn 27 in the summer so if the Falcons decide to throw big money his way, the contract will be justifiable. The Falcons need to get bigger, meaner, stronger, and more athletic up front. Osemele is the perfect man for the job.
Stefan Wisniewski (C)
The Falcons season in 2015 fell apart not because of the defense or because of the passing game dying, but because the offensive line fell apart with Mike Person failing to snap the ball consistently or block effectively at center. Ideally, the Falcons bring in someone to replace Person as the starting center, and Stefan Wisniewski has both experience in a zone blocking scheme and talent to succeed in it. He's not as quick as Person, but his experience at center and his ability as a blocker would make the offensive line as a whole improve. Person isn't a complete lost cause as he was a solid blocker at times and could be an answer as a stopgap at either left or right guard in 2016 for the Falcons.
Danny Trevathan (LB)
When looking at most top-tier defenses, one element usually stands out. Explosive edge rushers used to be the main priority for every defense to emerge into an outstanding uint. It remains as a key component, but not a total necessity. Look no further than the Carolina Panthers, who had aging pass rushers in Jared Allen and Charles Johnson playing significant snaps. Stout linebacker play has become essential in today's game. With teams depending on underneath throws to move the chains more often, three-down linebackers will become more coveted.
Successful defenses will usually feature two versatile linebackers. Luke Kuechly and Thomas Davis is a phenomenal duo. Bobby Wagner and K.J Wright have been excellent for years. The Super Bowl champions benefitted greatly from Brandon Marshall and Danny Trevathan flying around the field. Jamie Collins and Dont'a Hightower has emerged as one of the better duos. When people look at the emergence of Minnesota's defense, the speed of Anthony Barr and Eric Kendricks immediately stands out. All five teams have drafted extremely well in the linebacker department. Meanwhile in Atlanta, they've started overmatched undrafted free agents and injury prone veterans. With Justin Durant recently released, two linebacker holes need to be filled. The market for edge rushers isn't very appealing. Trevathan is entering his prime as one of the most complete linebackers in the league. He can cover, tackle in space, win at the point of attack, and play all three downs. There will be plenty of competition to sign him, which could scare Atlanta away. If they want to make a true statement though, this is the player that will help them do it.