Two great yet different combat flight sims to recommend are IL2 (buy the 1946 pack, has all expansions etc. ever released) and Battle of Britain II.
IL2 has craploads of different planes to fly and theatres to fly in. BoBII, as the name implies, concentrates to the Battle of Britain with 4 or so flyable planes only, but it shines in the size of the battles and the AI, which once you patch it up with the latest BDG patch is VERY life like (AI makes mistakes, tried to trick you, use historical tactics etc.) which easily makes up for the low amount of flyable planes.
Moving onto ground battles, I'd recommend the Close Combat series. They've started to re-release the games with new names and few new features. Top down view where you command your troops in WWII Europe. The games are old, but I still love them and go back to them once in awhile. Can't recommend them enough.
EDIT: Ow and welcome aboard.