Homeworld looked nice, sounded nice, but played... not so nice... Homeworld 2 plays far, far better, but doesn't have the awesome atmosphere of the original..
Now, here's something I totally forgot myself: Space Rangers 2.
(I made a nice post about it back in the days on the UQMF, but they're currently down for maintenance! I'll stick a link to it in here when it's back up, meanwhile:)
Space Rangers 2 is a relatively unknown adventure/RTS/spaceshooter/RPG hybrid from some crazy unknown russian developer, and happens to be quite like SC2 itself, but in a much more vibrant, in-depth universe (smaller scale!). Basically, you go around solar systems to make money by doing missions, mining minerals, finding artefacts, killing pirates, or doing piracy yourself. In a way, it's like Elite, only much more accessible due to a nice interface, the fact that it is 2d rather than 3d, and it's turn-based design (which is executed in an amazingly useful and nice way!).
Where the game shines (and its russian background shines through) is the adventure parts. Every now and then, you can accept an adventure mission where you need to accomplish a certain task, from participating in a violent flycycle race, to managing a ski resort, to saving a guy who has been kidnapped. Unfortunately, the writing in these adventure parts isn't top-notch, as the translation from russian to english is not so good. Also, if you manage to get jailed in SR2, it's not just "game over", no, you get to actually play through your sentence time in a nicely detailed ingame adventure game, including cockroach races and fights between inmates!
There's also some other parts to it, like a small and basic RTS part (one of the things that is splitting the SR2 community apart into those-who-like and those-who-hate), and a little action, melee-esque game.
At one point in time, an expansion was released that added new RTS maps, new adventure missions, and new equipment (hulls, special shields, new special artefacts). This was then picked up by Stardock, who polished the rest of the game (mostly writing) and are now selling Space Rangers 2 alongside with the expansion:
http://www.impulsedriven.com/sr2cMetacritic of the original, without-expansion for all you lazies:
http://www.metacritic.com/games/platforms/pc/spacerangers2dominators