I enjoyed KOTOR more than it's sequel, but both were fun. Obviously the Jedi Knight series was great (II rocked). I even enjoyed the old galactic rts-type...um...Rebellion? I tried to get X-Wing to run on my Vista PC but was ultimately uncessful. Galaxies was fun for a while.

On my PC presently I have Empire at War installed (along with several mods), and Battlefront 2. I've got a great many of them in jewel cases I've had since junior high (10 years ago).

There's just so many out there it's hard to pick the best.