Join Date: Aug 2010
Location: United Kingdom
County: South Lanarkshire
As with any form of disc, destroying the platter makes them 100% unrecoverable, so the scissors suggestion will definitely work. There are still devices around that read them, up until about 10 years ago most servers still had floppy drives as Windows Server 2003 needed one to install controller drivers and I still see kit that old quite regularly. You can buy USB Floppy Drives as well.
However, if you have absolutely no concerns about whats on them, you'll get some money for them on eBay. As they are no longer made and there is lots of old tech that still use them (E.g. old synthesizers and samplers) there is still a market for them, I sold a load last year.