I've always been a flight sim junkie, and these top 2 are still my favorites:
#1. Not to be confused with the re-release F4: allied forces (crapola !!!) is the best of the best, Falcon 4.0 (with super pack 3). It doesn't get better than this unless you actually attend OCS.
and another oldie but goodie but lacking in 'on ground activities' (also not to be confused with the re-release F/A 18 Operation Iraqi freedom (again simplified for the masses),
#2 Hornet:Korea- smooth as glass graphics, ultra realistic flight model and avionics but no real mission planning (the biggest disappointment of the game),
and my first league flight sim:
#3 Janes ATF (advanced tactical fighter) Not as much a sim as a game this one gives you bunches of different A/C to learn and really stable online co-op missions to fly with your friends.
Still I've bunches more that deserve honorable mentions:
A: Strike Commander- From the creators of wing commander your a mercenary commanding a squadron of pilots YOU hire as well as equiptment YOU have to buy (with earnings from missions YOU choose from rogue governments, privateers, and evil dictators. LOADS of fun and a pretty good sim (in 640X480 DOS).
B: Red Baron 3D- another ultra smooth online experience, kill your friends with a generous selection of the greatest A/C of WW1.
C: Janes IAF (Isreali Air Force) A very nice sim with some of the most memorable missions I've ever flown in any sim.
D: Janes F-15 A must have if your into flying the eagle (a nice touch is the ability to have an online friend fly with you in the back seat ( your R.I.O.).
I've about a dozen more but I'm sure you don't want to hear me call them crap.