From the electron's perspective, all superconductors are sort of perpetual motion machines. A perpetual motion machine is basically just any lossless kinetic system, so if you count electron flow in a loop of superconductor as a kinetic system, then it qualifies.

edit - These folk sell a 2MJ one - http://www.bruker-est.com/bas_special_applications.html

That kind of storage without the cooling requirements would be pretty useful...