I own both of those games too. I love the Dawn of War series as well, System Shock 2 is awesome, and you can't forget some of the Star Wars games like Jedi Knight 2 or Jedi Academy and KOTOR. I did buy Sword of the Stars a few months ago, and it's not to bad, another 4x style game.
Favorite Sci-Fi Games?

I just picked up X3: Terran Conflict. Seems like a good game, but it is proving to be a resource hog.

I recieved a free copy of X3 on Steam, and have yet to get it to run. So when you have played some, let me know what you think.

Since I got sick, I haven't had a chance to get back to the game. However, I was getting a bit annoyed with it because it seems to make the life of a newb needlessly harsh. I like EVE's newb missions much better. In fact, so far, I would have to say that the only advantage to playing X3 is the lack of monthly fees.
What are some of your favorite sci-fi games?
For me, I would have to say Sins of a Solar Empire & Galactic Civilizations 2. The first is better at simulating fleet actions, while the latter is more of a "galactic emperor" sort of game.
Anybody play these games or other sci-fi games?