For an unusual game, you might try these paper models of Golden Age Superheroes.
Poundland is the UK version of the US Dollar Store chains. They sell knock-off Lego superheroes and the Death Zap blog wrote a set of rules for them called Poundland Super Heroes.
Heroes Among Us is a pay-what-you-want game for quick play superhero skirmishes.
The Men and Supermen Role Playing Game is designed to allow super powered characters to fight along side normal characters. In doing this the RPG takes on what I think is one of the most difficult of tasks — creating a common scale between units of disparate strength.
Ed Walker has written a set of free wargames rules called Tabletop Titans. He writes:
BAM – POW – KAZOWEE. These are the sounds of super heros in action. Who could forget the wild brawls we all envisioned while reading our favorite super hero comics? Tabletop Titans is a game of miniature combat where players create super heros to do battle. Designed to be played on any tabletop or with one of the many types of terrain systems on the market Tabletop Heros provides all the rules necessary to create a unique super hero and pit it in combat against other superpowered beings. Tabletop Titans uses the ACTION combat system.