Total Annihilation was pretty much the apex evolution of RTS, though not as competitive as Starcraft. TA is also somewhere my top 10 greatest games ever list. Never really played it online however even though it was quite large during the time they released the add-ons.
As Lord_Kane already stated aptly, get
TA: Escalation after you've played a couple of skirmish matches and finished the campaign. Also google some TA mappacks. The game is very famous for having some of the best RTS maps you can play in Skirmish/Online mode.
On another note I remember Starcraft actually not being that good until a few big updates and with BW coming out when it then exploded. It pretty much became the final nail in the coffin for just about every other RTS game. It was basically THE e-sports game during a certain period.