In Dawn of War I usually go as the Imperial Guard or Eldar. As the Guard I deploy a rolling wall of guardsmen backed up by two leman russ tanks, a Baneblade and whatever else fills the cap. As the Eldar: Howling Banshees and council with farseer backed up by 3 squads of warp spiders and two fire prisms for artillery support. Surround and shred.
Otherwise: Soviets for their tesla coils & tanks in Red Alert, Nod for their obelisks and Kane in the Tiberium timeline and Mayans for their archers in AoE II.