A franchise left tackle or even a top notch interior lineman can make or break a team's success the same way a terrible tackle or guard can. Outside of the quarterback position, a solid player who will stick around for a long, long time protecting a quarterback's blindside is the most important thing a team can acquire.
Teams with long-term stability at the premier tackle spot typically don't have to worry about that side of the line at all. But not every team is blessed with stability along the offensive line, a unit that thrives on cohesiveness above all. In a perfect world, a team will have five consistent offensive linemen together for a long time.
This is not a perfect world, and most teams in the league are on constant lookout for ways to improve the play of the big guys up front. There is never a shortage of promising offensive line talent in the NFL Draft, but free agency isn't a bad way to go about it, either. It also happens to be a relatively strong class for both guards and tackles.
Below, we'll take a look at the best offensive linemen appearing on our top 100 free agents list.
Cordy Glenn, OT, Buffalo Bills
Nobody knows for certain if Cordy Glenn will actually hit the open market or not. But if he does, then seeing how said market responds to a legitimate franchise left tackle actually available should be something to see. Glenn has started 61 out of 64 games for the Bills over the past four years, and while he hasn't always been perfect, he's improved every season in the league. The Bills will do all they can to retain him so he can continue to give Tyrod Taylor excellent support from that position.
Kelechi Osemele, OL, Baltimore Ravens
Osemele has shown high level play at multiple spots along the offensive line, and this past season went from being referred to as a guard to being referred to simply as an offensive lineman. He started that final four games of the Ravens' 2015 season at left tackle, and was already considered the top guard candidate set to hit the open market. Now his value can be as high as an elite guard or even potentially a franchise left tackle, if the Ravens let him get to free agency.
Russell Okung, OT, Seattle Seahawks
Okung was heralded as the successor to Walter Jones on the blind side when Seattle selected him with the No. 6 overall pick of the 2010 draft. He showed some flashes in his rookie year, but has otherwise settled into an above-average left tackle, which made him a disappointment to fans expecting him to replicate Jones' Hall of Fame production. He's also prone to lingering injuries and drive-killing penalties, never quite living up to expectations.
Despite those concerns, Okung remains one of the better left tackles in the league and will surely get a nice-sized contract this offseason. A lengthy rehab from shoulder surgery might be a road block, but Okung has done enough to keep a starting job, whether it's in Seattle or elsewhere.
Alex Boone, OG, San Francisco 49ers
Boone is a dominant interior lineman who was also San Francisco's top swing tackle over the years. He has started games at left and right tackle and his value on the open market could vary greatly based on these abilities. Boone himself thinks he's good enough to be a top-flight tackle in the league and will target teams willing to pay him like one.
A dominant run-blocker who can shore up four of the five positions on the line at a moment's notice, Boone will hold value for any team looking to establish a running game. He's no slouch in pass protection either, and is a reliable, up-and-coming offensive lineman.
Mitchell Schwartz, OT, Cleveland Browns
The Cleveland Browns offensive line was inconsistent last season, but Schwartz played reasonably well. Center Alex Mack is expected to opt out of his contract and look for a new place to land, and if the Browns were to also allow Schwartz to walk, that would give them a great deal of uncertainty along the line heading into 2016.
The Browns allowed 53 sacks last season, but Schwartz turned in a solid performance over the course of the year. According to Pro Football Focus Premium Stats, Schwartz allowed three sacks and eight hurries all season. Schwartz, 26, has been consistent over his four-year career, and he would be a viable option for any team seeking a competent right tackle.
Evan Mathis, OG, Denver Broncos
Mathis was released by the Philadelphia Eagles last year due to an extensive injury history. This was despite him being a Pro Bowler in 2014 and an All-Pro selection in 2013. He was the team's starting right guard and he was among the best offensive linemen in the league when he was active. Now he's coming off a season in which he played in 16 games and started 12 for the Broncos, and played at a very high level. He's up there in years, but he's got momentum again and should find a new team.
Richie Incognito, OG, Buffalo Bills
After sitting out a season due to his part in the Miami Dolphins bullying scandal, Incognito was given a chance by Rex Ryan and the Bills. It was a very boom-or-bust signing, but Incognito panned out in a big way. He was among the league's best guards last season, and now he should have plenty of suitors. He's nearing the end of his career, but he clearly has a lot left in the tank given his strong 2015 campaign.
Jeff Allen, OG, Kansas City Chiefs
Allen, a second-round pick in 2012, has been a decent backup over the years but really showcased his value this past season. Playing in 12 games with eight starts, Allen showed he was more than the below-average player he proved to be in his first couple years in the league, and he showed a versatility that makes him a very valuable player. He can play both guard spots and he can kick outside if need be.
Stefen Wisniewski, C, Jacksonville Jaguars
Wisniewski isn't the player he once was with the Oakland Raiders, where he began his career as one of the most promising young centers in the NFL. After three strong years, he struggled through a torn labrum in 2014 and signed a one-year, $2.5 million "prove it" deal with the Jaguars.
He beat out second-year player Luke Bowanko for the starting role in Jacksonville, but was just OK in his one year with the young offense.
At age 27, another year of recovery from labrum surgery and rehab, which took up most of Wisniewski's 2015 offseason, will do him well. He is still a starting-quality player and could return to form as one of the better centers in the NFL.
Donald Penn, OT, Oakland Raiders
Penn has been a dependable left tackle for some time, and if Cordy Glenn gets extended or tagged by the Bills, Penn is suddenly one of the only options available to hold down the left side of an offensive line. The Raiders would like to keep him. He started all 16 games and though he's past his prime, he has a couple more seasons left in him.
Andre Smith, OT, Cincinnati Bengals
Smith was a hyped draft pick by the Bengals, but immediately came with baggage and concerns about his motivation and weight. But after a rocky start, Smith got things under control and he's become one of the more dependable starters on the team. Smith missed two games with a concussion last time and had 11 penalties, so there is still some baggage, but he's well beyond the point of being a burden.
Kelvin Beachum, OT, Pittsburgh Steelers
Beachum was a seventh-round pick back in 2012, but worked his way into the starting lineup and started all 16 games at the left tackle spot in 2014. He was among the top left tackles for much of that season, but he sustained a torn ACL just six games into the 2015 season, making his value on the market a big question mark. If a team is confident he'll recover, then he'll certainly get paid.
Brandon Brooks, OG, Houston Texans
Brooks is a priority free agent for the Texans, but if he hits the open market he should be appealing to teams in need of a starting-caliber guard. He has started at least 14 games in each of the past three seasons, and has had the most success at the right guard spot. At 26 years old, there is a ton of upside.
Ramon Foster, OG, Pittsburgh Steelers
Foster is getting up there in years, but he's started 87 games over the course of his career, including all 16 games as a guard for the Steelers last season. He could be seeking his last big payday and played quite well. The Steelers also have to deal with potentially losing Kelvin Beachum, so Foster just might be playing on a new team next season.
Manuel Ramirez, C, Detroit Lions
Ramirez is a veteran with a lot of wear, but at 33 years old he still has something to offer. He played in 16 games last season, but started just seven and has the distinction of being one of the only starting-caliber centers to hit the market this offseason. He's not the sexiest free agent pick up for a team that needs help, but he could be a value pickup for one lucky team.
Joe Barksdale, OT, San Diego Chargers
Barksdale was the best performer on a bad Chargers offensive line last season. He was the best player on that line and he knows it. He's a strong right tackle who can hold his own against all kinds of pass rushers, and is hitting the open market for the second time in as many years. He played in and started all 16 games last season, just as he did with the Rams the year before.
Mike Harris, OT, Minnesota Vikings
Harris will turn 28 next season and is coming off his first full season as a starter. He's hitting the open market at a good time because he had a very good season for the Vikings despite injuries along the offensive line. He started all 16 games, while previously he had started just five games for them in 2014.
Chris Chester, OG, Atlanta Falcons
Chester was signed as a last-minute replacement for the Falcons, and he was meant to come in and shore up the left guard spot until the Falcons could draft a replacement. But he ended up replacing Jon Asamoah at the right guard spot and played quite well until a shoulder injury forced him into struggles nearer the end of the season. Still, he's shown versatility and has potential going forward.