Compilations in iTunes.
My iPod's Albums menu was cluttered up with albums with only one or two songs. The Artists menu was cluttered up with slightly different name variations, such as "Julie Andrews" and "Julie Andrew and Rex Harrison". The answer to this mess is Compilations, or the "part of a compilation" setting in iTunes.Read more about it here; scroll down just a bit to "this week's Ask iLounge column".
I'm already pretty compulsive about getting album art onto all of my songs. Compilations add a whole new way in which to be obsessive compulsive about fixing my iTunes.