A discussion down the pub the other night reminded me of one of the only RTS games I've ever managed to really get into - Total Annihilation. Having spent years grappling with the likes of Z, the C&C series and so on, I remember what a breath of fresh air this game seemed like. No tedious resource harvesting - just plonk down your collectors and forget about them! Build- and order-queues! The D-Gun! And, lest we forget, the Core Contingency addon's introduction of the Krogoth - a hundred-foot universal weapons platform of a mech, capable of taking out entire armies all by its massive self and willing to take six nuclear missiles to the face before keeling over. The staggering array of carefully-balanced units, the gorgeous animation, and that soundtrack...I gotta find my install CD, I know it's around here somewhere.
(The other RTSs I've ever really liked are the Dungeon Keeper games. I miss Bullfrog terribly.)