The Short Stirling has always been a favorate plane of mine, but I think realy in the way of early War Buff's the following would help the most for the SEA and for the CT:
Beaufort
Betty or Nell
Il-4
Cant Z. 1007
The Beaufort is a great plane for an early war Buff it is very versatile, in that it is torpedo capable and carys for the time a contempoary bombload and defensive aramament, it was used in the PTO and in Europe and would fit well into many events and the CT.
The Betty/Nell, these would be last on my list in terms of priourty, since the only real diferance between the Peggy we have and them is spead which depending on model is around 20 to 40 mph.
The Il-4 is a must realy we do not have any Russian Bomber's yet and this plane was very important historicaly and would help fill a huge hole in the plane set, presently their are NO Early War Russian planes in the game.
Cant Z. 1007, this would add a new plane for Italy and a new capabality and a nice adation to the Med for events and the CT, used almost everywhear Italy faught from the Begining of the war to it's end and more capable than the SM 79 it would be a nice adation to the plane set.