Yay! At last, some responses.

I also liked Warhammer 40,000: Dawn of War too (and it's expansion pack as well).

One of the most refreshing games that I've ever played, even though the plot is just okay. Liked the gameplay a lot as it is something different compared to what most RTSes offer these days.
Also heard a lot about Homeworld too, even though I don't have it. Heard that it was one of the best RTSes from reviews of this game.