Below is a division-by-division breakdown of the key free agents for all 30 clubs. Teams are listed in order of their division finish. Also check out the Hot Stove Tracker for updates throughout the postseason.
NATIONAL LEAGUE EAST
New York Mets
Key free agents: Yoenis Cespedes, Daniel Murphy, Bartolo Colon, Tyler Clippard
The Mets have solid internal options across the board, with Michael Conforto and Dilson Herrera set to take over for Cespedes and Murphy, respectively, and some combination of Steven Matz, Rafael Montero and Zack Wheeler (once he returns from Tommy John surgery rehab) filling Colon's shoes in the rotation. Addison Reed and Hansel Robles are strong candidates to become the primary setup options if Clippard departs.
Key free agents: Jordan Zimmermann, Doug Fister, Ian Desmond, Denard Span, Casey Janssen
Joe Ross' emergence as a capable big league starter should mitigate some of the Nats' concerns if they lose either Fister, Zimmermann or both. With youngsters Michael Taylor and Trea Turner potentially able to fill the roles of Span and Desmond, respectively, Washington could save some money at those positions, while also getting younger.
Key free agents: Jeff Mathis, Casey McGehee
Among NL East teams, the Marlins are easily the least affected by the opening of the free-agent market, as they stand to lose only their backup catcher and third baseman. The question isn't so much who Miami will lose. It's who it will bring in to help boost an offense that finished 29th in the Majors in runs scored.
Key free agents: A.J. Pierzynski, Ross Detwiler, Edwin Jackson
The Braves will need to decide whether they're comfortable with Christian Bethancourt as their starting catcher. Pierzynski might not be back, and even if he returns, he'll be 39 next season and incapable of an everyday catcher's workload anyway.
Key free agents: Aaron Harang, Jerome Williams, Chad Billingsley, Jeff Francoeur, Justin De Fratus, Cliff Lee
The free agency of Harang, Williams and Billingsley coincides nicely with the arrivals of several of Philadelphia's top pitching prospects. Aaron Nola, Alec Asher and Jerad Eickhoff all debuted this season, and No. 2 prospect Jake Thompson, who came over along with Asher and Eickhoff in the Cole Hamels trade, could be ready for big league action as well.
AMERICAN LEAGUE EAST
Toronto Blue Jays
Key free agents: David Price, Dioner Navarro, Marco Estrada, Mark Buehrle (retiring), Mark Lowe, LaTroy Hawkins, Cliff Pennington
There aren't many teams getting hit harder by free agency than the Blue Jays, who will lose three members of their starting rotation. Among Toronto's top five pitching prospects, none figures to be big league ready next season. Marcus Stroman showed signs that he's an ace-caliber starter, but the Blue Jays will need to add some pitching depth around him.
New York Yankees
Key free agents: Chris Young, Stephen Drew
The Yankees' shortage of reliable right-handed hitters gets even worse when Young hits the market. Top prospect Aaron Judge, a 23-year-old power-hitting outfielder, could fill that role soon enough, but in the meantime, expect New York to be active in free agency, as usual. Meanwhile, at second base, Rob Refsnyder, who hit .302/.348/.512 in 16 games last season, could be given the keys to the position in Drew's absence.
Key free agents: Chris Davis, Wei-Yin Chen, Matt Wieters, Darren O'Day, Steve Pearce, Gerardo Parra
Davis figures to be one of the most appealing free agents on the market, and you'd expect Baltimore to do anything in its power to bring back the slugging first baseman. But the loss of Davis isn't the only potential void on the Orioles' roster. They also have issues to resolve at catcher, both corner outfield spots, the starting rotation and the bullpen.
Tampa Bay Rays
Key free agents: Asdrubal Cabrera, John Jaso
Tim Beckham showed a few signs that he could be an everyday shortstop for the Rays, but that might not preclude them from trying to re-sign Cabrera, who was one of their more reliable performers. The loss of an on-base threat like Jaso could hurt, too, and Tampa Bay -- which boasts one of the league's best pitching staffs when healthy -- will likely be looking for an offensive jolt after it finished second-to-last in the AL in runs scored.
Boston Red Sox
Key free agents: Craig Breslow, Rich Hill
The Red Sox won't be losing much to free agency. There are legitimate questions as to whether they should bring back Hill, who posted a 1.55 ERA in four starts but turns 36 in March. Otherwise, Boston's recent youth movement should be on full display across the diamond next season, but don't be surprised if the Red Sox go after a big-name starter to boost their rotation.
Video: Price, Greinke highlight a strong free agent class
St. Louis Cardinals
Key free agents: Jason Heyward, John Lackey, Matt Belisle, Randy Choate, Carlos Villanueva, Jonathan Broxton
Heyward leaving would leave a huge void, but the emergence of Randal Grichuk and Stephen Piscotty would severely lessen that blow. Lackey proved that, at 36, he still has plenty left in the tank, and the Cardinals may try to retain his services.
Key free agents: A.J. Burnett (retiring), Aramis Ramirez (retiring), Joakim Soria, J.A. Happ, Sean Rodriguez, Antonio Bastardo
The Pirates' core group of homegrown talent remains intact. But given the sheer volume of free-agents-to-be on the 2015 roster, there is bound to be some shuffling. The departures of Burnett and Happ could be mitigated should prospects Tyler Glasnow and Jameson Taillon arrive on the scene in Pittsburgh next season.
Key free agents: Dexter Fowler, Fernando Rodney, Austin Jackson, Jason Motte, James Russell, Clayton Richard, Trevor Cahill, Chris Denorfia
Fowler leaving would sting, but it's in the bullpen where the Cubs will be hardest hit by free agency, as five relievers are set to depart. There was always plenty of room for improvement in Chicago's bullpen, however, and this offseason gives Theo Epstein and Co. a chance to tinker.
Key free agent: Kyle Lohse
Regardless of the fact that Lohse finished the season in the bullpen for Milwaukee, his departure serves as a reminder that the Brewers could use some help in the middle of their rotation. Taylor Jungmann looked impressive in his first big league season, but the Crew needs to start building a deeper rotation around him.
Key free agents: Sean Marshall, Brayan Pena, Burke Badenhop, Skip Schumaker
Like the Brewers, the Reds won't be affected much by free agency. They'd like to bolster their bullpen in front of Aroldis Chapman, with the possible departures of Marshall and Badenhop. But otherwise, they should be free to spend elsewhere without worrying about losing players.
Video: Scott and Dan discuss offseason free agents
Kansas City Royals
Key free agents: Alex Gordon, Johnny Cueto, Ben Zobrist, Alex Rios, Ryan Madson, Chris Young
The World Series champs needed a front-line starter and a second baseman midseason, so they went out and acquired Cueto and Zobrist, who filled those voids well. Problem is, Kansas City will be faced with those same issues in the offseason, and no one in the organization seems ready to step in. On Wednesday Gordon declined his option, and the Royals declined their mutual option on Rios, leaving two holes at the two corner outfield spots as well.
Key free agents: Mike Pelfrey, Blaine Boyer, Neal Cotts, Brian Duensing
Minnesota has a solid young core of offensive talent, but the club needs pitching depth. And although Pelfrey has struggled for the past three seasons, his departure still signifies the Twins' need to find some rotation help. The pending arrival of the club's No. 2 prospect, Jose Berrios, could be a nice start.
Key free agents: Mike Aviles, Shaun Marcum, Ryan Raburn
Few big league clubs will be affected less by free agency than Cleveland. And that should work nicely for a team that has developed a solid crop of strikeout-heavy starting pitchers.
Chicago White Sox
Key free agents: Jeff Samardzija, Alexei Ramirez, Gordon Beckham, Geovany Soto, Matt Albers
Samardzija struggled in his one season on the South Side, and the White Sox hope 22-year-old Carlos Rodon will take Samardzija's place behind Chris Sale in the rotation. Chicago declined a $10 million option on Ramirez on Wednesday, opening up the shortstop job, as well. The Sox hope top prospect Tim Anderson can fill that role eventually. But Anderson isn't big league-ready just yet, meaning the club will need to find a replacement for Ramirez in the offseason.
Key free agents: Alfredo Simon, Alex Avila, Rajai Davis, Joe Nathan
Detroit's influx of young pitchers mitigates the concern that they'll be losing Simon. And if Avila departs, James McCann and Bryan Holaday have proven themselves more than capable behind the plate.
Los Angeles Dodgers
Key free agents: Zack Greinke, Brett Anderson, Jimmy Rollins, Howie Kendrick
Greinke's career year in 2015 coincided with the opt-out clause in his contract, and the 32-year-old right-hander opted out on Wednesday. The Dodgers will undoubtedly aim to re-sign Greinke if he does, but he'll be in demand. The potential loss of Anderson -- not quite as high profile as Greinke -- could prove costly as well, and Los Angeles' already shaky rotation depth stands to take a major hit if neither returns.
San Francisco Giants
Key free agents: Tim Lincecum, Ryan Vogelsong, Mike Leake, Joaquin Arias, Tim Hudson (retiring), Jeremy Affeldt (retiring)
Expect the Giants to be active on the free-agent front in search of starting pitching. Four San Francisco starters had their contracts expire this season, and it's no secret that the Giants are lacking reliable options behind Madison Bumgarner.
Key free agents: David Hernandez, Jarrod Saltalamacchia
The D-backs aren't losing any key pieces, but their rotation still lacks depth. It'll be interesting to see which hurlers Arizona chooses to pursue in free agency.
San Diego Padres
Key free agents: Justin Upton, Ian Kennedy, Shawn Kelley, Brandon Morrow, Clint Barmes
From an offensive standpoint, Upton's departure is massive, but it allows Wil Myers to shift from center field to left, at the very least, boosting the Padres' overall team defense. In that vein, San Diego will need to decide if a Melvin Upton Jr./Travis Jankowski platoon in center is the answer. And the Padres will also likely need to sign at least one starting pitcher with the impending departures of Kennedy and Morrow.
Key free agents: Justin Morneau, Kyle Kendrick, Michael McKenry
The Rockies declined their $9 million option on Morneau, which signifies a transition to Ben Paulsen at first base. Colorado was already in need of starting pitching even before Kendrick became a free agent, and the Rockies hope top pitching prospect Jon Gray, who debuted in August, can be part of the solution.
Key free agents: Yovani Gallardo, Colby Lewis, Mike Napoli, Will Venable
It's hard to envision Lewis leaving the Rangers, and he has expressed his desire to return. Still, Texas will likely need to boost the middle of its rotation by either adding a starter or re-signing Gallardo. The Rangers also will get a boost when Yu Darvish returns from the Tommy John surgery he underwent in March.
Key free agents: Colby Rasmus, Scott Kazmir, Tony Sipp, Oliver Perez, Joe Thatcher, Chad Qualls
Rasmus' torrid postseason boosted his stock, and it remains to be seen whether the Astros will attempt to retain him (or go after another outfielder). They could very well be content to simply hand over more playing time to Preston Tucker and Jake Marisnick. The potential loss of Kazmir may be even more impactful, and Houston could be in the market for a No. 2 or 3 starter if he leaves.
Los Angeles Angels of Anaheim
Key free agents: David Freese, Chris Iannetta, Matt Joyce, Shane Victorino
Freese's free agency presents the Angels with a question as to whether the organization feels Kaleb Cowart can be an everyday third baseman. Chances are, the Halos will aim to bring back Freese or at least look elsewhere for help at the hot corner. Their other free-agent losses all appear to be fixable internally, but don't be surprised if the Angels focus on bringing in another big bat.
Key free agents: Hisashi Iwakuma, Franklin Gutierrez
Iwakuma stated his preference to return to Seattle, but it's still unclear whether he and the Mariners will work something out in free agency. If he departs, it would leave a big hole behind Felix Hernandez in Seattle's rotation.
Key free agent: Edward Mujica
Mujica and his nearly $4 million salary will come off the books, and the A's would be wise to reinvest that money in their bullpen after they posted an AL-worst 4.63 relief ERA in 2015. Of course, that isn't Oakland's only area of weakness, and despite the absence of any significant roster subtractions, the A's might still be busy this offseason.
AJ Cassavell is a reporter for MLB.com. Follow him on Twitter @ajcassavell.