RTS recommendations.

Has anyone got any personal recommendations for good RTS games? I'm looking for something with good AI, and preferably on the PC (although any system except PS2 is OK). The last RTS I played was the original WarCraft (and I was crap at it).

After quite a long break (since early March), I'm finally getting back into the nitty-gritty of camera control research (solver optimizations). I'm coding up the little test framework for it, and hope to some some very un-exciting screens shortly.