Hard Drive Disposal

You can degauss them yourself, and then send them off to a professional for disposal where they will be mechanically crushed and the materials recycled.

If you do not have the ability to deguass them, and the data is very sensitive, you could at least sanitize/zero all of the disks prior to sending them for disposal since most companies cannot 100% guarantee the data will not be intercepted.

If you are willing to process the data on every hard drive prior to sending them off, you would have many options, but I am assuming you would just like to be rid of them.

Look into On-Site disposal solutions such as the ones Nexcut offers, they will come to your facility and crush/shred/drill holes into tape media, hard drives, disks, anything.

If all your worried about is wiping the data off the drives then please see this previous post:

How should I securely wipe data from a hard drive?

There already is a question addressing both wiping and disposal: How do I destroy a hard disk?