Corey Hart is going to get paid more than most people expect, because power is getting more scarce than it has been, and if he's healthy, he's got power. He'd be a good pickup for the Sox, but he might end up getting offered more than we would prefer to give a guy who missed all of last year.
If Ellsbury leaves, then a good guy for the Red Sox to target for a cheap AAA pickup would be Dan Robertson from the Padres, a sort of combination between Nava and Pedroia.
He's a short OF, bats RH, can play all 3 OF spots, steals some bases and gets on base. Too old to be a prospect, and another PCL hitter, and short, so he likely wouldn't cost much and wouldn't be anything more than another guy to keep in AAA for depth. He could be a guy who gets a shot to come up for a while if Bradley starts out really badly and needs to get sent back down for a while. Rather than tying up a major league roster spot with a Bradley insurance policy, we could have one in AAA.
He represents depth for the Padres too, so they wouldn't just give him away for nothing, but considering his height and age, they shouldn't ask for much. He seems like he'd fit in well with the Red Sox organization, and I care a lot more about his OBP than his height.
In addition to Crain and Madson mentioned above, another possibility for the bullpen might John Axford, if he gets non-tendered. He supposedly made some mechanical adjustments after joining the Cardinals, and looked like a guy with a real live arm in the postseason. If he does get non-tendered, he will be looking for a job as a closer I'm sure, but we should keep tabs on him in case that doesn't work out for him.
I suppose my Hot Stove wish is for another season of "deep depth," which is what Cherington preached all season and which worked fantastically well. No need to change that. Let's have another season of average or better players at every position, a relentless offense with no easy outs, a deep pitching staff with lots of internal options, lots of roster flexibility, and more "deep depth" throughout the organization.