I have been loving Shieldwall, a strategy game where you and your Roman legion attempt to kick the crap out of other Roman legions!
This game reminds me of a 3D Starcraft, with (thus far) a lot less complexity. You start with one base and attempt to take others from other CG teams!
More bases result in more resources for you to spend, so get to work!
I bought it on Steam for less than $10.