X-wing was my first space-sim and I got immediatly hooked, but Tie Fighter definitly surpassed it!
Starlancer stood out to me as well, compared to other space-sims of that time, because of the fast-paced combat, and the excellent developing tactical missions and story. I never played freelancer as I'm a joystick-guy, too bad for me probably.
Independence war, Edge of Chaos. The atmosphere of this game was incredible, involving story, open-ended world and excellent combat - definitly one to remember.
Darkstar One was good, a little repetitive, and the last part of the game your ship was extremly overpowered, but without a doubt it's one of the better space-sims of newer times.
Freespace 2; and not just because its gone open-source.
Wing Commander 3&4.
X-Wing and TIE Fighter.
That's about it. Not really a fan of the X series or Darkstar One myself. Freelancer isn't really part of the list. No joystick = not a flight sim. --- To the everlasting glory of the Infantry: Shines the name of the Rodger Young! (Read the book)
For me the best are Freespace2, Freelancer, X3 Reunion. One thing I don't like at first in Dark Horizon, is the adjustments you make on your spaceship for each mission(shiled/weapon/speed power), I would like it carried over or changing energy while in the space like in Freespace2, and obligues you to look for dif strategies because of the ship you made troughout the game.
I'm looking for Evochron Renegades, seems nice, I'll play the demo but it seems not many know about it tough the reviews in the site are good. Maybe to good compared with the User Ratings. Having a cockpit is awesome, really like it.