-WWII Online (aka, Battleground Europe).
MMO FPS ($14/m) with very dated graphics but when it comes to WWII aircraft sim combat I'm not sure much else compairs. The gameworld consists of most of europe with terrain taken from satellite photos and most of the major towns/cities are there so you can fly to any of them (assuming you don't get shot down). Everything from engine RMP control to extending wing flaps is there, planes handel like in real life (eg, turn to hard and lose control) and there is a very detailed damage model where parts of your plane can be shot off (losing part of your wing not being as bad as losing your whole tail section) or you yourself can be shot and thus have problems controling the plane assuming your not dead.
-ARMR II
While more of a modren combat sim then a flight sim, it still might be worth checking out if you are intrested in the aircraft that are in the game. You still have fule, wing flaps and RPM but flight wise it doesn't compair to WWII Online. It also has a very large map (a few hundred square miles) with a very high level of detail that will tax your system. It also includes a editor (units, not terrain) that will allow you to put units around the map and give them orders such as "When X unit enters X area head to X location and do X action". It has MP, but public matches are a total mess. There are however many "clans" that work towards a more realistic gameplay style to the point of weekly training sessions.
-Engima Rising Tide
Best open ocean WWII surface navel sim I've found. Includings ships (ranging from PT boat to destroyers) and subs. I think the slient hunter series would be better for subs though.
-eidt-
-X3
Yes, Sci Fi space fighter sim, but being on sale at steam you might be interested. While not a ture sim (you constantly bleed speed until you stop) it looks pretty damn nice. Look it up on google if you are interested (I suggest X3: Terran conflict and skip X3) and if you just want the sim part look for cheats and mods.