Maybe I'm not paying attention (likely), but Derek B. told us about something in iTunes 8 that I'd never seen before -- you can organize your music in Grid view by genre, and when you do, there are some pretty good-looking icons that show up for each genre. I especially like the Blues and Jazz icons (nice nod to the old Blue Note Records in there), but all of them have a pretty neat vibe, summing up each genre as best they can in a colorful little box.
Of course, there will always be more music out there than boxes to put it into, and so Derek B has started up a Flickr group to come up with icons for some of the more obscure genres out there. Replacing the icons is pretty easy to do, and there's even an app that will let you do it with ease -- just find the icon you want, and tie it to your genre. As you can see above, if you don't have an icon for the listed genre, it'll show off your album art (and just like iPhoto, mousing over the picture will let you flip through whatever albums are in there). It's kind of a weird thing to add into iTunes (and it's kind of tough to line them all up -- it's too bad iTunes won't pull down genres for music it recognizes from the iTunes store), but odds are we'll see these icons pop up more later, so getting them all lined up now is probably worth it.