Superman (It's Not Easy) is by Five for Fighting. As far as I know the Foo Fighters have never sung it, but they have similar names, so it's easy to mix them up.
Not all of these are directly about Superman, but they mention his name:
Sister Hazel - Superman
Dave Matthews Band - Where Are You Going?
Three Doors Down - Kryptonite
Lazlo Bane - Superman (the theme to
Scrubs)
REM - I Am Superman
Bob Schneider - Big Blue Sea
The Dixie Chicks - Godspeed
Zoomway (no, not the same one

) - Lois Lane
John Mayer - 83
Goldfinger - Superman
Here are some that say something about heroes in general:
Matchbox 20 - Real World
Remy Zero - Save Me (the theme to
Smallville)
Mariah Carey - Hero
Enrique Iglesias - Hero
Chad Kroeger - Hero (the theme to
Spider-Man)
Bif Naked - Spaceman
Bonnie Tyler - Holding Out for a Hero
That's all I can think of right now.
~Anna