Every time I buy a pack of empty CDs, they come with this transparent cd shaped plastic and I never got around what to do with them. Some very old music sheets and I had beautiful new costers in less than 20 minutes!
*For best results, use only a glue stick, not liquid white glue!*
Just take any double sided image you have (comic strips would also look awesome!), cut them the size of the cd, cut out the center hole too and just carefully glue between 2 plastic disks (don't over do it with the glue!). Let dry! (Mine were not completely dry in the pictures!)
Use the cd container to keep your coasters neatly!