Must Play RTS
Warhammer 40,000: Dawn of War
Rise of Nations
Warcraft III: The Frozen Throne
Command and Conquer Generals

Recommended
Rise of Nations: Thrones and Patriots
Homeworld 2
Ground Control 2

More RTS...
Age of Mythology: The Titans
American Conquest
Axis and Allies
Battle for Troy
Blitzkrieg
Cold War Conflicts
Command and Conquer Generals: Zero Hour
Crusades: Quest for Power
Desert Rats vs Afrika Korps
Empires: Dawn of the Modern World
Highland Warriors
Impossible Creatures
Korea: Forgotten Conflict
Lords of Everquest
Medieval Lords: Build, Defend, Expand
Nemesis of the Roman Empire
No Man's Land
Northland
Once Upon a Knight
Perimeter
Praetorians
Squad Assault: West Front
The Gladiators: Galactic Circus Games
The Lord of the Rings: War of the Ring
Time of Defiance
War Times
Warhammer 40k: Winter Assault
Warlords Battlecry III
Warrior Kings: Battles
Wildfire
World War II: Frontline Command