If you are still looking for a way to make use of those old CDs you may have stocked that are no longer of use to you, here is something you may want to check out. Bruce Munro was able to come up with something interesting, making use of about 65,000 old compact discs and turning them into artsy looking water lilies.
The old CD water lilies are part of his lighting installation over at the Longwood Gardens in Pennsylvania. Rather than make use of other power-requiring lighting sources or even LEDs, Munro makes use of the water lily CDs to render the needed lighting conducted from the sun to illuminate the garden.
While not all people may have that much CDs on their end, the project should inspire some people to somehow apply the same concept, even on just a smaller scale.