The summer swap season had its unofficial Opening Day in Chicago on Thursday. For the price of a $3 Ventra Card, Jose Quintana made his move from the South Side to the North, with the Cubs giving up a huge haul to the neighboring White Sox for the controllable services of a guy who can stabilize a surprisingly wobbly rotation in the bid to repeat.
So that was fun, and there's plenty more where that came from.
What follows is not a list of predicted swaps but, rather, five deals that would seem to have value for both sides. You can of course chime in or come up with your own in the comments section, because, remember, baseball's general managers are always looking at internet articles and comments sections for advice on how to do their jobs.
1. RHP Sonny Gray from the A's to the Brewers for OF Corey Ray, RHP Luis Ortiz and LHP Nathan Kirby. 
The Brewers countered the Cubs' acquisition with a small-but-significant swap for left-handed reliever Tyler Webb. Could they go after the market's other obvious controllable starter? As voiced by their All-Star representative, closer Corey Knebel, the Brewers' players are hoping their surprising work in the first half compels the Milwaukee front office to do something.
"It's not up to us -- I'm hoping they see something," Knebel said. "They're in there every day with us, and they see how we're coming together, I think. I know they're going to make some tough moves."
General manager David Stearns is not going to punt on the long-term picture, but he does have incentive to do right by his clubhouse in the here and now. Gray, under arbitration control through 2019, serves both tasks. The cost, of course, would be punitive, but Gray is capable of giving quality innings to a starting unit whose struggle to go deep into games in certain stretches taxed an otherwise effective bullpen. This proposal costs the Brewers, as determined by MLBPipeline.com, two of their top five prospects, as well as another from their top 30. Gray has a recent injury history but retains high value in these market conditions.
2. LHP Zach Britton from the Orioles to the Astros for RHP Francis Martes and OF Kyle Tucker
The bottom line is that the Astros, in their search for a bankable, top- or near-top-of-the-rotation type to prepare for the postseason, don't have a ton of options on the table in this particular market. But they could remove pressure from their current rotation by taking a bullpen that has been heavily taxed this year and turn it into a super 'pen if they can compel the O's to move Britton, who is under arbitration control through 2018.
Like the Indians with Andrew Miller and the Cubs with Albertin Chapman last year, this move would be all about October. Britton only recently returned from a forearm strain, and it might take a couple weeks for him to prove to clubs that he's still worthy of a big trade package like this one. But his velocity is still strong, and he could be a difference-maker in a World Series run.
As for the O's, Britton's rising arbitration price is a luxury they can ill afford given other payroll demands and the state of their farm system. They can take advantage of a weak closing market with this kind of swap.

3. RHP Player Page for David Robertson from the White Sox to the Nationals for 3B Drew Ward and LHP Jesus Luzardo
If this trade sounds familiar, it's because it nearly happened during the Winter Meetings. The Nationals, ultimately, weren't willing to pay the price of Robertson's remaining contract ($25 million total from 2017-18), and they've been paying the price for not pulling the trigger ever since. They remain reluctant to take on significant salary for their very obvious need for relief help, but, look, two-thirds of Roberton's $12 million salary will be off the books by the Deadline, and we're trying to win a World Series here, people!
In a market with a dearth of quality relief help and with the White Sox very obvious sellers, the Nats ought to investigate the possibility of expanding this pursuit on the South Side, perhaps involving a hot hand like veteran Anthony Swarzak (2.41 ERA, 1.00 WHIP) or a more controllable (and costly) option like Tommy Kahnle.
The Nats should be able to acquire relief help without giving up top prospect Victor Robles, and they do have the option of trying to find a midseason diamond in the rough in this light market. But they are too good in every other element of the roster to play games with the 'pen. They need some semblance of certainty, and, until or unless Britton hits the market, Robertson is the most certain closer piece readily available.

4. LHP J.A. Happ from the Blue Jays to the Indians for OF Greg Allen and LHP Ryan Merritt
Toronto's approach to this Trade Deadline will be especially fascinating because, while the AL Wild Card, at the very least, is still in sight, its organizational age and continued inability to get to .500 is impossible to ignore. If the Blue Jays do sell any assets, they have multiple expiring pieces to dangle without going too deep into an actual rebuild. But Happ's continued excellence after missing some time with elbow issues and affordable contract (he'll make $13 million again in 2018) make him an extremely valuable trade chip despite, well, the aforementioned elbow issues. This could be a sell-high moment.
Were the Blue Jays to dangle Happ, the Indians are an obvious fit, and not just because these front offices are so obviously intertwined. The Indians aren't likely to add to their rotation unless it's an arm that would conceivably start in a postseason series for them, and Happ would qualify as a No. 3 behind Corey Kluber and Carlos Carrasco. That he happens to throw with his left hand (the Tribe's rotation is entirely made up of right-handers) adds to his allure. He's the kind of target that would probably allow the Indians to keep their top two prospects, Francisco Mejia and Triston McKenzie. Allen, their No. 7 prospect per MLBPipeline.com, is a really intriguing speed/defense/leadoff type, and though Merritt's raw stuff limits his ceiling, the Blue Jays know too well how effective he can be when he's hitting his spots and not "shaking in his boots."

5. OF J.D. Martinez from the Tigers to the Dodgers for RHPs Imani Abdullah and Trevor Oaks.
This column has featured arms aplenty, in part because this is setting up to be a buyer's market for bats (particularly outfield bats). We could reach a situation in which some sellers are simply trying to move money without expecting much in return. But even in this environment, Martinez, a pending free agent, does stand out as an impact acquisition. How seriously the Dodgers, who could certainly use his production from the right-hand side of the plate, would pursue such an option ultimately depends on how much they trust Joc Pederson (whose struggles against lefties have been pronounced), breakout utility man Chris Taylor and Yasiel Puig. But obviously the injuries to Alvin Toles, Andre Ethier and Franklin Gutierrez have impacted the outfield depth, and Cody Bellinger has been filling in at first for the injured Adrian Gonzalez.
The market conditions will drive down Martinez's price tag from the top-tier realm (right-hander Yadier Alvarez and outfielder Alex Verdugo are the Dodgers' top two prospects), so a 20-year-old pitching piece like Abdullah and a depth piece like Oaks (though currently nursing an oblique injury) might make sense.