Let's call a spade a spade: Album covers are just marketing tools. They're pretty effective ones, at that -- a great album cover can make you spend your hard-earned money on an album that wasn't even any good. (Or, at least, they could, back when that was how we expanded our music catalogs.) But great album covers can be more than just marketing materials -- when they're really great, they can be works of art in their own right, interacting and feeding off the music they are meant to represent.

The last 15 years have been a fruitful time for album covers, with artists seeking different media -- from laser-cut glass to neon signs to hand-drawn cartoons to optical illusions -- to express and engage the music. Above, browse our favorites from the new millennium. We recommend spending some time to gaze at each one. After all, it might be the final era in which they matter at all.