The Greatest Band or My Greatest Band? Depend on the moment but the greats of (i hate to say it) yesteryear....
Floyd, Purple, Zeppelin, Beatles, Rush, Hendrix, Sabbath
getting more recent...
Maiden, Nirvana, Metallica, U2, G'n'R
As for songs again depends on the moment but
One - Metallica (i would put Am I Evil but it's a cover!)
The Prisoner - Iron Maiden
Stairway to Heaven - you know who!
Paranoid - Black Sabbath
Voodoo Chile (slight return) - Jimi Hendrix (also All along the Watchtower but it's a cover!)
Aaaah to many to mention....