A slew of interesting players are entering their contract years for the first time, as they'll reach six years of Major League service at some point during the season.  Josh Hamilton, Miguel Montero, Mike Napoli, Erick Aybar, B.J. Upton, Andre Ethier, Shaun Marcum, Brandon McCarthy, and Anibal Sanchez are examples of such players. However, if arbitration-year extensions were not so common, the following players would also be headed for free agency after 2012 by virtue of accruing six years of service.

Starting Pitchers

• Scott Baker's extension three years ago with the Twins included a $9.25MM club option on the 2013 season, which has a good chance of being exercised if he can maintain decent health.
• Chad Billingsley inked an extension with the Dodgers one year ago, paying $26MM for his first two free agent years or $37MM for his first three.
• Jon Lester signed a deal with the Red Sox three years ago that became a standard for his service class.  That contract bought out Lester's first free agent year with a club option on another, although the option is voided if he is traded and has finished first or second in the Cy Young voting in 2012 or '13.
• The Marlins' Ricky Nolasco is notorious for having an ERA unworthy of his peripheral stats, and the team owes him $20.5MM over his first two free agent years.
• The Rays bet on James Shields four years ago, getting three club options on a pitcher with less than two years of service.  They've got a potential ace at reasonable option prices for '13 and '14.
• As a Scott Boras client, Jered Weaver seemed unlikely to sign an extension, especially after taking a tough stance in arbitration.  However, Weaver took a hometown discount last summer and is signed through 2016.

Position Players

• Imagine the added drama for the Red Sox if Lester and Dustin Pedroia were both heading into walk years.  That could've been the case, but Pedroia signed four years ago, giving the team control for up to three free agent seasons.
• If you think Troy Tulowitzki's November extension was massive, picture what he'd be looking at as a 28-year-old free agent after 2012.
• Angels second baseman Howie Kendrick was pretty close to free agency, signing a deal last month buying out three free agent years.
• The D'Backs' Chris Young signed four years ago, giving up one free agent year and an option on a second.

Relievers

• The Reds made Sean Marshall an offer he couldn't refuse this month, as he didn't expect much more than three years and $16.5MM in free agency.
• Royals closer Joakim Soria signed four years ago, and still has a pair of club options on his first two free agent years.
• The Blue Jays' Casey Janssen and the Cubs' Carlos Marmol would also be entering contract years had they not signed extensions.

Five veteran starting pitchers were traded last summer: Edwin Jackson of the White Sox, Jason Marquis of the Nationals, Erik Bedard and Doug Fister of the Mariners, and Ubaldo Jimenez of the Rockies.  Jackson, Marquis, and Bedard were in contract years, while Fister and Jimenez are under control through 2015 and 2013, respectively.  The White Sox were 3.5 games out in the division, the Nationals 12 out in the wild card, the Mariners 15 out in the division, and the Rockies 10 games out in the division.  

These five deals demonstrate the difficulty of predicting summer trades — we don't know at which point each team considers itself out of contention, and there are always a few surprising non-contenders.  By normal criteria of long-term value, no one thought prior to the season that Jimenez would be dealt, regardless of the Rockies' fortunes.  The new collective bargaining agreement adds another wrinkle, in that players traded midseason are no longer eligible for draft pick compensation.  Even if they're not contending, the Nationals have added incentive to retain Jackson this summer, because they could make him a qualifying offer and potentially receive a draft pick, while another team cannot.

All that said, assessing potential non-contenders is a good starting point in predicting trade candidates.  It can be an offensive exercise, given the optimism spring training brings.  Still, the Orioles, Athletics, Mariners, Royals, Mets, Pirates, Astros, and Padres are unlikely to be popular preseason picks for the postseason.  The Blue Jays, Indians, White Sox, Cubs, Dodgers, and Rockies also have more than their fair share of question marks.

That pool covers half the teams in baseball.  Cross-reference that with starting pitchers who may be eligible for free agency after the 2012 season, and you get Scott Baker, Bedard, Bartolo Colon, Kevin Correia, Jorge De La Rosa, Ryan Dempster, R.A. Dickey, Gavin Floyd, Jeremy Guthrie, Francisco Liriano, Derek Lowe, Paul Maholm, Marquis, Brandon McCarthy, Kevin Millwood, Brett Myers, Carl Pavano, Jonathan Sanchez, and Jake Peavy as names to watch.  The Mariners will continue to receive inquiries on Felix Hernandez, though a deal involving Jason Vargas is more likely.  The Mets' Johan Santana and Mike Pelfrey will generate interest if they're pitching well, though Jonathon Niese is the long-term target.  We'll hear plenty more about the Astros' Wandy Rodriguez and the Cubs' Matt Garza.  The Padres' Tim Stauffer is an interesting under-the-radar target, as someone under control through 2013.  Similarly, the Indians could move Jimenez in the right midseason deal if they're out of contention. With a strong first half, perhaps the Pirates' A.J. Burnett could be flipped.  We haven't gotten much into contenders with rotation depth, but rumors involving Braves righty Jair Jurrjens could resurface.

If Felix remains unavailable, should we expect any true aces to hit the market?  The Giants have a pair in Tim Lincecum and Matt Cain, if they dig a huge first-half hole.  The Rays could check the market on James Shields, and David Price is under control only for one year beyond Shields.  The Brewers and Marlins appear primed to contend, but if either team bombs, impending free agents Zack Greinke, Shaun Marcum, and Anibal Sanchez will be popular names.