In my opinion, the Hero System, and Champions in particular, is the best system there is for running superheroic and heroic-type games. In my experience, no other game system allows the creation of super-powered characters with such a wide-ranging, but also well-defined and fairly unambiguous range of powers and abilities, coupled with a reasonably clear and simple combat and action resolution system. Of course, such a flexible system can be abused by players who know too much, but that is something which (I hope!) bitter experience has, by now, taught me to avoid...
I've run a number of games using Champions over the years, details of many of which can be found through the links below, along with assorted other Champions and Hero-related material.
An original new animated kids TV show concept from my brother.
Also, be aware that this site is constantly under construction, so it is entirely possible that things will be changed or added to without warning or notification (though it will be very rarely that anything is actually removed).