iVolume: "With iVolume you can bring all your iTunes songs to the same loudness... results of iVolume are much better than those of the built-in 'Sound Check' function in iTunes.... iVolume does not change any data of your audio files, so there is no loss in quality. iVolume simply adjusts the 'Volume Adjustment' slider that you can find in the information dialog of iTunes for every song."
This is a $7 shareware app. It sounds very clever. I'm definitely going to give it a try. Volume adjustment on the iPod is a bit of a nuisance and "Sounc Check" has a poor reputation. I want to see if the iPod will honor the iTunes volume adjust setting!