I have been asking my self the same thing when I move an apartment and found that I have 79 CD's I do not need. Well, I figured some I would use again ( mainly t.v shows and movies I downloaded ) but still I had to many, so I looked up for good uses and I found two.
1. Use them as coasters
2. Cut them to 1 sq CM and glue them to a Styrofoam ball, vwalla ! You got a disco ball!
Here are more tips I found
http://www.hintsandthings.com/musichall/CDroms.htm
