Depends on the specific genre really. I'd say you are best off using a combination of Plastic Chaos Warrior Maruaders, and maybe some Plastic Imperial Guard. The Marauders are all muscle bound figures with archaic weapons and very little clothing on their torsos, where as the Imperial Guard will give you some more weapon and clothing options.
Another option would be an old 40k Chaos Cultist conversion kit. It was a mix of Ork, Zombie and Mutation Sprues. The Ork arms and torsos would work particularly well for creating overly muscled Heroes / Villians.
Combining the plastic sprues with Heroclix figures will give you even more options. There was a wonderfull Lobster Johnson conversion with a plastic GW head in the pulp forums a while back.