According to SI.com (via MLBTR), the Red Sox recently tried to reacquire the Marlins' Hanley Ramirez:
At one point this winter, the Red Sox made a play to re-acquire Marlins superstar Hanley Ramirez, league sources tell SI.com. But while the Marlins listened to Boston's overtures, talks were quickly scuttled and it appears there's very little chance they will be revived as Florida isn't anxious to trade its best player.
The Marlins were said to be most interested in a centerfielder, and it's believed Boston's promising young centerfielder Jacoby Ellsbury and talented pitching prospect Clay Buchholz were among those mentioned in a potential package for Ramirez, who began in Boston's organization before being traded to the Marlins after the 2005 season in the deal that sent Josh Beckett and Mike Lowell to the Red Sox.
The price would be high, but Ramirez has proved to be one of the best in the game. I think it'd be pretty far fetched to get Ramirez back, but the Sox do have the prospects to pull off the deal. According to SI, the Sox are happy with Jed Lowrie at short and may have played Ramirez in center.