Oh well, i guess there's some more to add.

Westwood Studios. What id Software made for action genre, Westwood made for real-time strategies, starting with Dune 2 and continuing with Command & Conquer series. And they made quite a few other good games...

And then, there's definetely old good Microprose with games like Civilization, X-COM, etc. And X-COM 1, 2, 3 are among my favourite games of all time.