Obsolete and dead hard drives have been piling up for 7 years in a wardrobe I want to empty. Here they are ready for execution; one had to be dug out of a Time Capsule:
The ones that I know held sensitive data (unencrypted backups mostly) I wiped via cradle mount.
Then it was sledgehammer time. The lawn was a bad idea — even by my neglectful standards it made a mess.
The best results came from angling drives on concrete, and using short strikes to fold the drive:
A one pass wipe and a sledgehammer might not stop the NSA, but it should suffice for Best Buy recycling.