I thought hard disk speakers looked cool so I've made one.
the hdd which I've used is an old Seagate (631mb capacity - yeah.. Really old.)
Don't do this with new/good hdd's because once you open that drive's case, you can't expect to use it as a storage drive anymore.

"hard disk speakers" are nothing more than eye candy. they sound pretty crap and you need an amplifier to work it. they're quite easy to make though.. - if you have a dead hdd lying around, might as well play around with it =D