For data CD’s. Destroy the surface. I usually run a scissor blade across them. Or, snap them in half and there is the microwave trick. As @worriedguy is about to tell you. :-)
If they are music cd’s give them to your local goodwill. If they are informational cd’s take them to your local shredder company. (Our city has a yearly document shredding day, where you can watch them being destroyed).