France:
D.520: France's best fighter, good enough to perk farm with and useful in scenarios.
Germany:
Do217/He177A-5/Ju188A-2: Gives the Germans a mid war bomber, filling a gap.
Me410: Interesting and fun German multi-role aircraft
Finland:
Brewster B239 Buffalo: The Finnish community deserves a bone.
Italy:
C.R. 42: Fills the need for an early war Italian fighter, also would be fun in that it is a biplane.
S.M. 79-II: Main WWII Italian bomber.
Japan:
A6M3: Mid war Japanese Navy fighter, fills gap in A6M lineup.
B6N2: Mid war Japanese torpedo bomber, gives the Japanese a competent torpedo bomber.
D4Y2: Mid war Japanese dive bomber, gives the Japanese a competent dive bomber.
G4M2: Early war Japanese bomber, fills a gap.
J2M3: Mid war Japanese Navy Interceptor, fleshes out Japanese planeset and fills a gap.
Ki-43-II: Early war Japanese Army Fighter, fills a gap.
Ki-44-II-Otsu: Mid war Japanese Army interceptor, fleshes out Japanese planeset and fills gap.
Ki-61-I-Ko or Ki-61-I-Otsu: Mid war Japanese Army fighter, fleshes out Japanese planeset and fills gap.
Soviet Union:
LaGG-3: Early war Lachovkin fighter, fills gap in Lahovkin lineup.
I-16-24: Early war Russian fighter, fills gap.
Pe-2: Mid war Russian bomber, fills gap.
SB-2: Early war Russian bomber, fills gap.
Tu-2: Late war Russian bomber, fills gap.
Yak-1: Early Yakolev fighter, fills gap in Yakolev lineup.
Yak-7: Early-mid war Yakolev fighter, fills gap in Yakolev lineup.
United Kingdom:
Beaufighter: Early-Mid war RAF attack plane, fills gap.
Firefly: Adds a RN attack plane, filling a gap.
Mosquito B.Mk IV: Early Mosquito bomber, fills gap in Mosquito lineup.
Mosquito B.Mk XVI: Late war Mosquito bomber, fills gap in Mosquito lineup and adds a new perk bomber.
Wellington B.Mk III: Early war RAF bomber, fills a large gap.
United States:
B-17E or F: Earlier B-17, fills a gap in the B-17 lineup.
B-25C or D: Early war American bomber, fills a large gap.
F6F-3: Earier F6F model, fills gap in F6F lineup.
P-39D and Q: Widely used American fighter, broadly useful.