Are you looking for a Skirmish game or an RPG?
Skirmish you have Super System, Super Mission Force and Slugfest! all from Four Color Studios. SMF is a less crunchy Super System, Slugfest! is a co-op/solo game.
RPG there is GURP, Icons, Mutants and Masterminds, Marvel, Super Action Role Play (from Four Color studio) and many more.
As a note the Four Color Studios games are by Scott Pyle an active poster here and will usually answers questions for his games. I am also a big fan of his skirmish games. I have Super Action RP game but have not had a chance to play yet.