My RTS interests have been consumed with playing and watching Starcraft 2, I dip into old favourites like early C&Cs and Supreme Commander but they just don't feel as solid and diverse as SC2, I find the gameplay ends up too linear and predictable. Although SupCom has a more epic, large scale feel to it which I enjoy.
I know you said RTS but have you tried turn-based such as Galactic Civilization 2? It has a similiar concept as Sins with more freedom to move around space, and very intelligent AI.