kaizokurisu has some cool images of a Super Mario Subwoofer on his Flickr page.
Super Mario Subwoofer
My friend offered to build me a subwoofer from scratch, so I came up with this design. This is of course the question mark block and brick block seen in the original Super Mario Bros.! He built it to the correct dimensions and then I painted it. I am satisfied with how it turned out!
Check his Flickr page for more images.
Link via Make:Blog