Now before everyone goes nuts, there are no suggested names, and I highly doubt you'll be seeing the Rock or Stone Cold become a fixture of the WWE anymore. There are a few names, though, that feel like potentials to me:
1) Vince McMahon - He's on every week, clearly doesn't plan on retiring any time soon, and may be building up towards a WrestleMania storyline that involves him. Plus, there's the rumors that ECW is going to be gone/changed soon and Smackdown may be changing as well, so Vince will be doing things already on-screen most likely. That's just as good a reason to think he WON'T be the new GM, though, but Vince is always a safe option to bank on similar to HHH winning a title.
2) Vickie Guerrero - They're continuing with this Teddy Long probation storyline, she's teasing that she may be a GM for Smackdown, and blah blah blah. I hope she isn't their choice as they could do much better, since Vickie's act has worn old and she was already the GM of Raw for a little bit. Still, like Vince above, she's a safe bet to bank on as a potential.
3) Jim Ross - He will probably still be out for a few months, but he will return. The problem is that they seem to like their current setup for commentators and despite how losing JR would hurt them in that department, they haven't been killed so far. Grisham sucks ass in my opinion, but the only way he's going to learn is by doing (if he learns at all; I'm personally a much bigger fan of Josh Matthews and think he has 10x the potential) and I wouldn't be surprised at all for them to say that they want Grisham/Striker, Lawler/Cole, and Saxton/Matthews to remain the teams. JR has proven that he's great on the mic, that everyone loves him, and that he knows what he's doing when it comes to cutting a promo, so why not put him in place as the babyface GM of Raw? It could be a great thing. JR contrasts from Teddy in that he's not trying pathetically to be "cool", and he contrasts from the Guerrero/Regal/etc school of General Managers in that he wouldn't be screwing people over and abusing the power in storylines. I think people would enjoy watching JR be a fair and honorable calm GM as a change of pace.
I don't think we'll be seeing Bret return full time, nor do I think we'll be seeing someone jump ship and return ala Jim Cornette or Paul Heyman. To me, those 3 above are the only possibilities right now. But, as always, we'll have to wait and see.