Another tip for iTunes users that's unrelated to album art... The Sound Check option in iTunes used to do (maybe still does) a miserable job of equalizing volume. If you're unhappy with the results of Sound Check, try equalizing the volume levels of your songs using iGain / mp3gain. It's a freeware app that does a good job. It's not especially quick but the results are well worth the wait.
http://altosdesign.com/iGain/