I only tend to get rid of them once they've failed, in which case I normally pull them to bits to get the magnets and motors out (I still love pulling electronics to bits for handy components!). FWIW, be very careful if you do this as it's very easy to snap the neodymium magnets together and trap your fingers... it hurts.... a lot!
If you've getting rid of drives, I'd use some secure erasing software (loads out there for free) to wipe it clean. You could then sell it on, give it away... or just chuck it/destroy it.