Star Wars: X-Wing Alliance was one of the best Star Wars games ever, especially for the space combat-sim variety.
While I also voted for Star Wars: Jedi Knight II: Jedi Outcast, I think it's sequel Jedi Academy is better. I mean... Jedi Outcast has a much, much better story, but Jedi Academy was so much more fun.
The first Knights of the Old Republic was incredible for its time, too. A great game and an awesome Star Wars tale.