And in Non-D20, I enjoyed the Worlds of Wonder, and second edition Superworld put out by Chaosium. Simple percentile mechanics for everything, character generation may take a while, but play is simple. Superman may not be possible, but anything without Invulnerability probably is...
Some interesting stories: The big, dumb, Mighty Mauler in the sample adventure included with Superworld attacked PCs with giant chunks of concrete ripped up from the pavement. My PC had an 18 strength, but nothing near his... He did have good armor, though. So when the MM clobbered him, he was uninjured, but trapped beneath the weight, and unable to move! Fortunately, he had one level of Burrowing skill (his only power which required energy), and managed to dig his way out from under the pavement... AFTER the fight was over!
In another episode, he learned that being invulnerable didn't always solve the problem... The bad guys had a 50mm machinegun, hammering away at our heroes. My PC charged, and his armor easily absorbed the hits... Unfortunately, the Knockback rules made it so that, every time he ran forward, he got knocked back farther than he ran by the machinegun fire, so he couldn't ever reach the NPC Mooks. He was forced to play "distraction" while the other PCs sneaked in and clobbered all the baddies!
Such is life in Superworld...