A moderate volume, seriously I don't see what the big deal is with having music loud enough to make your ears bleed. This way I can enjoy the music at a reasonable level without disturbing anyone enough for them to complain.
Sometimes I raise the volume to a level where I can experience music in a better way (some rock songs from Creed and Linkin park have a lot of sounds you can't really appreciate on a volume other then very loud).
Sometimes I'm walking down the street and I hear music being played from a building fairly far away clearly, whats the point in having it that loud?
God I sound old
but I'm serious.