I seldom bother to look at the links in the footer of a webpage, but this time I'm glad that I did. If you click on the Build link at the bottom of the Last.fm pages, you'll be whisked off to build.last.fm—a site full of "free extras built by the community to extend your Last.fm experience."
Many of them look pretty cool, but the one that I liked the best was Gijsco's Desktop Generator. This free application is full of customizable options that allow you to tweak everything just the way you like it: from canvas size to individual album size. It even lets you select what pool of data to draw the albums from, whether it be from your Top Overall, to All albums listened to in the past 3/6/12 months. The result is a beautiful collage of album covers that make for a stunning desktop wallpaper or page background.
I settled on a simple grid of 16×16px album covers, randomly drawn from the pool of albums I've scrobbled from in the last year. Here's a full-scale screenshot showing just a portion: