I can second that Mutants and Masterminds is a great game for superheroes - and even more if you have need for a cinematic game at lesser power levels.
I have run MnM as Space Opera, Pulp and now Supers. The cool thing is that the game's sidebars let you bring the game closer or further away from its D&D roots to fine tune it to your taste. It really makes it worth more than the $32 price tag. (a lot of people say they were first put off by the game's thin 192 pages, but realized they got their money's worth later.)
As far as running the two different ranges of supers you mentioned, MnM handles that in the same game by a variety of ways. First, a more "mundane" super hero can stock up on feats, which are the lynch pin to adding an edge to your character in the game. Second, MnM is built on the assumption that a player can claim that hard training and education can allow even a totaly "non-super powered" human access to super power to represent their edge. For example, Batman isn't a mutant, but his fine honed reflexes, training and focused intellect allow his player to buy the "super powers" of Combat Senses, Super Dexterity, and Gadget to reflect that his still a league above normal people.
To be fair, I haven't checked out the other d20 super games on the market. I have heard some people say they they think Silver Age Sentinels handles some things better and some things worse than MnM, and that most people prefers SAS's original rules system (Tri-Stat) compared to the d20 conversion.
I think all the supers games have reviews on this site, so check them out.
There is also Deeds, Not Words and perhaps another one I missed (forgive me if that is so.)
I can tell you with all sincerity to avoid "Foundation." The game was released very early in the d20 rush and it shows.