Laurie,
I use the numerous free AOL CDs and others that have been somehow wronged during a CD-R process and sand down the data(shiny) side with a fine grit sandpaper. Apply Createx monotype base and then use the Createx colors to create an image for a monotype.
My 8th graders loved the idea of sanding the discs and drawing on them. You can also use a water soluble crayon (Caran D'Arche, e.g) or water color pencils(gives a softer, less intense image) and run through an etching press, a brayer or the back of a wood spoon. Working on a circular shape presents all sorts of interesting thought processes in the kids as well and some exciting images.
Check out: http://www.createxcolors.com/ and http://www.monoprints.com
for further info and inspirations. Hope this helps.
Dennis