Red Baron. The one and only. The best ever flight simulator when compared to similar products of it's time as well as it's radical ideas - I mean, it had polygonal models for crud's sake! And you could fly through the whole war in pseudo-dynamic campaign mode! From three sides of the war, and you could even paint your airplane as well as request squadron transfers and stuff... it is a great game even today, as soon as the immersion hits in I actually can't find it in myself to care about how crude the graphics and sounds are compared to today's standard (and they aren't even that bad IMHO anyway).
Grand Prix 2, the bestest ever formula 1 game when compared to similar products of it's time as well as the jump from previous versions. Also by many considered to be bestest ever F1 game period. Who cares about fugly sprite pit crew, drivers and cars being from 1993 (or 1994? I can't remember...) and graphics being limited to 800x600 when the sounds kick ass like no tomorrow, gameplay is pretty much unmatched and the cars still have slick tires and no nancy boy traction control (or, well, the driving aids are ther ebut they are more of a hindrance as soon as you learn to drive without them...)?
These two are perhaps still played by some, I would be amongst them if my current GPU would be actually VESA compliant. Though I doubt that their userbase would be as active as FS2(_Open) has, but anyway.
Also, X-Wing series of games counts as one of the legends that just keep on going.