Audio Normalization
Audio normalization lets you keep the volume at slightly saner levels. When sounds get too loud, it reduces the volume, and when it's too soft, the volume is increased a little. Audio normalization makes for a bit nicer listening.
You can also enable fades for songs. Fades are especially nice when skipping to the next track or pausing, as the transition is more natural and pleasing to the ear.
Download ALSong for those subtle differences that make listening to your music a nicer experience.