LucasArts impeccable Battlehawks: 1942 gets my vote. It's less a flight sim and more of a first person shooter in the air (although some basic flight sim rules do apply).
It was one of the first flight games I ever thought worked vastly better with a mouse than a joystick (A10 Tank Killer was the other). The manual was gorgeous, not only detailing the missions but outlining the historical perspective and peppered with first-person accounts and historical photographs.
I highly recommend it.
There was also an M4 Sherman simulator in the vein of M1 Tank Platoon but I never played it.
