Battlezone - A brilliant blending of first person tank combat and RTS gameplay. A really incredible game.
Krush, Kill n Destroy - A really well done C&C clone, solid campaigns, great soundtrack, cool setting.
Dark Reign - A well done sci-fi RTS with some of the best AI around, also has a great soundtrack from acclaimed Mechwarrior 2 composer Jeehun Hwang.
Nexus: The Jupiter Incident - A tactical fleet battle game, really really good.
Blitzkrieg - World War II strategy game with a lot of depth and a crazy amount of content. Really solid, challenging game.
Conquest: Frontier Wars - Space based RTS with a focus on battling across multiple fronts and maintaining supply lines. Really cool game.
Grey Goo - Sci-fi RTS from the remnants of Westwood. Solid RTS that plays a lot like C&C, however the 4 included factions are all really creative and unique. Godly soundtrack too.
Kohan: Ahriman's Gift - Considered by many who've played it to be the finest RTS ever made, a really unique, deep and challenging game that removes almost all the micro management from RTS and instead focuses on the larger picture and wide strategy aspects. Highly recommended.
Cossacks: European Wars (
or any of the others in the series) - If you enjoyed Age of Empires but thought it was too shallow and small in scale then Cossacks is your new jam.