Tristan Perich's 1-Bit Symphony is an electronic composition in five movements on a single microchip. Though housed in a CD jewel case, 1-Bit Symphony is not a recording in the traditional sense; it literally "performs" its music live when turned on. A complete electronic circuit—programmed by the artist and assembled by hand—plays the music through a headphone jack mounted into the case itself. The album is available here for $29.
To hear the music, all you have to do is plug in your headphones to the side of the case, flip a switch, and the electronic symphony begins. It's pretty fascinating, and part of Perich's idea is that each person gets a unique performance (the chip is using pulses and assembly code to actually perform for you). Perich has some other fascinating projects-- including the group Loud Objects, where he and two fellow artists solder circuits live, creating melodies as they assemble works on stage.