In no particular order, all these guys know they're stuff and I always look for their contributions:
Kev357th. Widwewing and Guppy, Kev for Spitfires, I was trying to find his thread about the seafire in the game being one of the rarest going, Great resource for spits etc, Widewing for a very indepth overview of WW2 aircraft as whole, from Fuel to ammo to types and sub types, A great resource for AH as a whole.
Guppy for his images and writing style, he has a knack of writing the history in such a way as bringing it alive and giving you a sense of immersion.
There's a few others but those three mentioned above are top notch contributers and the AH community as a whole are lucky to have them on here.