Llamatron. The very name brings a tear of joy to the eye of even the most cynical gamer.
Jeff Minter's seminal Robotron 2084 clone (full name : Llamatron 2112), where you must guide a laser-spitting llama (or camel, in two-player games) through level after level of psychedelic mayhem, rescuing beasties (sheep, goats, camels and the like) while cheerfully annihilating hordes of barking mad aliens. What other game challenges you to combat a loo-roll-spitting toilet, a sheepipede, bananas, coke cans, rizla packets, houseplants and YaK alone knows what else? It was originally released as shareware on the Atari ST and was later ported to the PC.
Jeff also wrote Tempest 2000, Attack of the Mutant Camels, and Metagalactic Camels Battle at The Edge of Time, and many others on the Vic-20, C64, ST, Amiga and various "commercially challenged" consoles.