1) "Chuck Yeager's Air Combat" - 3 wars, 6 flyable planes, simple flight model, 2D graphics, fits on a single 1.44 Mb floppy, tons of fun!
2) "Air Warrior" - 3 wars, about 56 flyable planes, player-controlled tanks, flakpanzers, jeeps, and trucks, carrier landings, bombers, torpedo attacks, online flying that is just downright addicting!
3) "Jane's Fighters Anthology" - USNF and ATF all compiled together into a sim that is just downright fun to play for even the most unskilled sim pilot.
4) "EF2000" - Its as if I'm actually there...
5) "Hornet: Korea" - it could be the ultimate flight sim, if only the 2D graphics were a bit better. I love the video tutorial - I wish other sims had it.
6) "Flanker" - the ultimate hard-core military combat sim. Fly it, if you have the guts.
And the ultimate submarine sim: SSI's "Silent Hunter". Think of it as a flight sim in the water.