Is this really an RTS? Great series, personally my favorite is Civ IV, but they are, of course, TBS instead of RTS...
I've also heard of Company of Heroes, like a WW2 rts game, any good?
Very, very good. Quite probably my favorite RTS game of all. The battlefields have stunning detail, with units taking cover in ditches, or artillery craters (that you just blew into the landscape) or inside crumbling, destructible buildings, you have the ability to employ tactics beyond the standard rock-paper-scissors model, and it avoids some of the micromanagement that I feel bogs down a lot of other RTS.
Some other good ones are:
- Supreme Commander (or Total Annihilation, though it's a bit old now - you could also try the freeware remake called Spring.)
- Homeworld (a unique space RTS based around carrier fleets and protecting your mothership, very cool.)
- Starcraft 2 (a really great sequel to one of the best RTS of all time, I'd even recommend the original.)
- Medieval 2: Total War (not purely an RTS, as it's a hybrid with TBS elements, but the real-time combat is some of the best, at least for melee-era warfare. Just pick the era you most enjoy, all the Total War games are good - except the most recent Empire and Napoleon, imo.)
Those are the ones I generally play.