There are lot of "Lite" versions of games that are out there. My two faves are those for White Wolf's Exalted and Lite BESM. Though you will have to whip up some monsters for the combat and both are downloadable from the net. With more work on your part, you could also use a template character version of Mutants and Masterminds
Exalted Home Page, Click on the downloads link to find the quickstart rules
BESM DL Page, Scroll down to find the fast play rules
The Exalted DL looks very nice and comes with some exotic background and encourages players to do outrageous stunts, which will avoid your neophyte players from hearing the dreaded "No." word. The classes are pretty well defined, the mechanics simple, and I think the game offered the GM the choice to use either d6s or d10s, but don't quote me.
The BESM Lite game will offer a lot options to the players, uses 2d6 and is also fairly loose. The sheer amount of options may turn some people off, however, may turn some people off and some of the powers are only listed, it's sort of in the GM's ball park to really define them.
If you have MnM, all your players need is one d20. While there will be more prep time, you players will never have to learn what hit points are about, one less mechanic out of the way. If you follow the MnM's lead in their core rule book, you could easily design some Level 5 templates and give people options to modifiy them, then you are off.
[edit: I just found out that BESM has also put up a FastPlay rules set for their superhero game, Silver Age Sentinels -- have fun]