Robots
Remember when Dr Robotnik/Eggman used to take fluffy bunnies and turn them into his mechanised minions in Sonic 1? That was a great plot for a game and Sonic hasn't been the same since the designers forgot about the 'free your friends' concept and went with the Chaos Emeralds instead (why are we looking for those, again?). Again taking cues from nature's own designs, the robot characters were so iconic too - the Buzz Bomber, Crabmeat and Caterkiller characters were superb and the series is all the poorer for their loss.
But Sonic isn't alone in his robot-fighting plight. Ratchet and Clank have robot enemies that look great and satisfyingly fall into their component parts when shot with big guns. And old-school classics like Impossible Mission and Flashback have robots to avoid/defeat.
Giving gamers robots to shoot may lack the imagination or thrill of more fleshed out (ho hum) enemies, but robots - and especially BIG robots - certainly make it into our book of cool.
Above: Sonic 1 and 2, Ratchet and Clank, Impossible Mission, Flashback, Coded Arms