What to do with old CDs / DVDs

Hey guys,
I have a bunch of old / unneeded CDs / DVDs that it seems like a pity to throw out. So I'm thinking of what I could do with them, something useful. So far the only idea that came to my mind is to use them as a sort of reflector in some DIY lighting fixture, it should work pretty well. But I have a few hundred of these disks and surely I don't need hundreds of lighting fixtures.

So I thought maybe some of you can come up with some brighter ideas, or share your experience, most people must have found good solutions by now. Help the environment, too, albeit a tiny bit. What do you say?