My best guess is that Cleveland is the most plausible partner for reasons that have well fleshed out here. Their #22 pick is reasonable compensation for the Bears IMO in light of what they could do in the draft and the salary cap restrictions that are freed up. The Brownies get, if they are willing to pay him, their future franchise QB (reaching for Tannehill @ #4 to keep him away from Miami or KC) and their franchise RB in effect with their 2 1st round picks. The Bears, in return for accepting a lesser but still decent RB corps, get another 1st round pick and millions of dollars in freedom from salary cap for FAs, Urlacher, Cutler, etc. Just think of what this could mean on draft day next week.
Couples in now realistically in play and he is the best physical fit for the team as a dominant 3-down plug-and-play franchise 4-3 DE. He's a physical freak who has Peppers v2.0 talent/power/skill and is the only 1st round guy who isn't truly a "tweener" between DE and OLB in measurables. Trading up from #19 for him via a 2nd rounder (gets you to ~ #11) or a 3rd rounder (gets you to ~ #14/15) makes him eminently draftable and allows Izzy to be used as a hybrid DE/DT who can play inside and out in rotation, especially for run defense which is his best skillset. Yes, there's a risk that Couples' "motor issues" are a concern but as others have pointed out the Bears is about the best situation for him to dispel those doubts (which were also raised about Peppers and Mario in the past). Couples would be playing on a dominant, almost freakish DL with known motivators in Marinelli and Lovie pushing him, and with his idol/mentor Peppers also kicking his ass. That line would be as good as Detroit's and Buffalo's IMHO.
You'd still have the #22 pick as well. Trading it down to the latter 1st or even upper 2nd would net you back the 2nd/3rd rounder you gave up for Couples and still prob also allow you to get Konz (pref.) or Zeitler. With Konz, you know have the Bears future franchise Center who can play OG in the meantime if Cutler still wants Garza snapping him the ball in 2012. Spencer is then unneccesary either this year or next which also frees up a few million more in cap space. And you would still have a pick in each additional round to grab a LB, a WR, and a DB.
I'd take that deal in a heartbeat at this point over a holdout or a whiny, pissed off Forte and future cap problems. Pure conjecture of course...probably 10% chance at most any of this happens, but just a scenario that seems possible and appealing.