Dammit, he didn't take the bait. There goes all of my fun!
Amazon is the place I usually get album cover art. What CaptainABAB said is true, but there is an even easier way is add album art in iTunes: Use the button in the lower left (looks like a rectangle with an arrow at the top) to open the artwork drawer. Go to the Library and highlight the group of songs you want to modify (easiest if you sort by album and use shift-left-click to define the tracks). Go to Amazon (or wherever), show the album art, left-click and hold, drag to the album art section of the Tunes window, and let go. It should modify all of the tracks in question.