what useful or creative things do you do with old CDs?

I use them in my garden to scare away the birds. I also use them for plant holders. I crochet around them and then put them under the plants.

I was going to hang them behind my Christmas lights this year, to reflect the lights, but I never got around to it. Glue two of them together with the blank side out, put a string or piece of yarn through the hole and knot it at the edge to keep it from hanging sideways. They also make good, if funky, coasters. You can glue yarn or fabric to them to absorb moisture and decorate them. I'll watch this discussion because I have a ton of them, too and I'd like to find ways to use them.

I saw a site a couple of years ago that had pictures of crafts people had made from them. Some of them, like an irridescent dragon, looked really great! I also have a friend who did his entryway walls in a sort of CD mosaic. Maybe not what you were looking for, but, maybe this will give you some ideas that more closely suit your tastes.