(American Analog Set: Know by Heart)
Clutter for OS X works well. I’m not so into its core usage (putting little CD icons all over your desktop), but it’s the easiest way to get album covers into iTunes.
I’m not sure why Apple doesn’t offer this capability themselves, using images from its Music Store. Overall, there ought to be more integration of the Music Store in iTunes. I want to be able to control-click on a track and be able to search the Music Store for similar songs/albums or for other albums by the same artist or for other songs on that same album. Hell, why not charge 10 cents to download cover art for tracks not bought from the Music Store (with the caveat that Apple need not run the transaction through until the next time the user makes a purchase, so that it overcomes credit card processing fees that would otherwise make this a loss-leader).
For albums “not in stock”, Apple could redirect users to Amazon and skim a referral fee. Either way, the user gets what he wants and Apple profits: musical symbiosis.
Integration could be inobtrusive and useful. That’s a pretty rare combination when it comes to advertising nowadays.