My humble wish is that all future aircraft fill in gaps in the scenarios we run, or would like to run.  Here are my top 3 theaters of war that are missing 
important aircraft:
Battle of BritainGerman:Ju 87B-1 (or B-2)
He 111H-3
Do 17Z
Bf 110C-4 (not the fighter/bomber variant)
Bf 109E-7 
British:Spitfire Mk II 
Hurricane Mk II 
I know someone is going to ask why I didn't include the Ju 88A-1 since RAF fighters have a hard time catching the A-4: from what I have read the A-4 was actually slower than the A4, so be careful what you wish for! 
Eastern Front 1941-1942:Russian:I-16
Yak-1
Yak-9
LaGG-3
Pe-2
Tu-2
German/Finnish:Ju 52
Ju 87B-1 (or B-2)
He 111H-3
Do 217
Bf 109E-7
Bf 109F-2
Bf 110F
Buffalo
PTO 1942-1943:American:Buffalo
TBD Devastator (Midway)
B-17E
B-24D
F6F-3
Japanese:Ki-43
Ki-44
Ki-45
A6M-3
Ki-21-IIa/b (Japanese bomber/transport)
G4M
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Ok, there's my list!  If I had to choose one from each theater, it would be these:  He 111, Pe-2, and G4M.  I would also say that, besides the He 111, the Russian and Japanese aircraft take priority over the rest.  
