What to do with a bunch of old hard drives?

I have a friend who took out the magnets from a bunch and uses them on her fridge.

That’s what I do too, they make great fridge magnets and are good for magnetizing tools.

Here in the Seattle area, we have many computer recycling places. We also have a large enough market for used PC parts that we can support a lot of stores reselling those things. Yes, people will still buy a Pentium 4 with 512 MB of PC100 and an 80GB IDE!

Alternatively, a friend of mine runs the local chapter of a charity that takes old equipment like that, puts it together into working systems, and donates them to schools, elderly, and low-income households.

So I guess it depends on what the local market for old PC parts is.

Please don’t throw away old electronics.
There’s all kinds of poisonous, nasty stuff in there. If you live in a civilized part of the world, a little searching will turn up an organization that responsibly recycles electronics. Check out the Basel Action Network for more information. If you live in a non-civilized part of the world, it’s probable that unscrupulous folks are dumping e-junk somewhere near you, where its gnarly rare-earths are seeping into your groundwater. Nice, eh?
If there’s a Best Buy near you then you can take the drives there for recycling:
http://www.bestbuy.com/site/Global-Promotions/Recycle-FAQs/pcmcat174700050009.c?id=pcmcat174700050009
I strongly recommend that before you drop off drives anywhere to be recycled, you first destroy the data. You can drill a hole in the platters if you’re so inclined. If you have a Linux live CD handy, you can put the drive in a computer, boot the computer with the CD, and type “sudo shred -zvf /dev/sda” (assuming that the drive to be wiped is the only one in the computer, it will probably be /dev/sda).

If you’re a hacker you can chuck 4 of those drives into an old PC case and make a backup server, or some other application that needs a bunch of relatively-slow storage. You could host a local Debian mirror. There’s plenty of uses for a little extra storage if you’re that kind of creative.
You can take the drives apart. There’s some neat stuff inside, solenoids, electromagnets, and the platters are nicely balanced and have good bearings. If you’re mechanically inclined there are some cool parts to play with. Some people just take the top off, spin up the drive and toss stuff in there to watch it go flying. There’s no accounting for tastes.
Just be sure to responsibly recycle the parts you don’t use. It’s really only the electronics in a hard disk that are dangerous, but the case and platters are made of materials that can go in regular recycling (cases are usually cast aluminum, platters are coated glass or plastic or aluminum).
If you haven’t guessed, I’m the guy @jerv was talking about. I think. He might know two different people who are embroiled in this kind of nonprofit work for all I know, but if so he hasn’t introduced us!

Thanks all for the wisdom. I think I’ll take at least one of the apart for the magnets, as @laureth first suggested.Just because it will be fun to take one apart.

The suggestion by @rexacora… recycling through Best Buy – is the fate for the others. THanks all.