I will start it off by saying my top choice would be to see a Midway MD-88 or MD-87 made from Gemini. We haven't seen too many MD-87s and Midway was an early and key operator of the type. A Delta Widget 727-200 would be awesome too.
As far as a new mold, I know a lot of people want an MD-11, which I would love to see in American colors.
I could think of a hundred for this, but I would love to see a couple of variations on current molds, too, like I'd like to see a 1/200 DC-8-73 and a DC-10-40.