But seriously, I would go outside and smash them to bits with a hammer. Don't know if that's environmentally friendly or not but I've always wanted to do that.
You can always buy an external hard drive case (make sure it's compatible with a laptop size hard drive), then connect the laptop hard drive to your current machine and wipe the drive.
-Clean the drives using DBAN, minimum 3 passes
-Open the drives up, get the awesome magnets
-Take to Best Buy to recycle, I think they'll accept 3 items per day per person
I took in a bad router to Best Buy. The guy at the front said just to leave it on the customer service counter. They'll take anything electronic, just be sure to wipe or destroy any hard drives that had sensitive data, even if you erased it.
We've always reused the old hard drives with the next computer, and inevitably needed something that was forgotten about on there some time later so it's worked out.