See Mexican Art and Folk Art - a site you probably wouldn't take your
students to....but one where you can get lots of images for your PowerPoint.
I added a link to the Masks from Larry's paper mache mask lesson -- and a
link to the Bolivian tin masks to the foil tooling lesson. Check the artists
shown to see which ones are suitable to your needs. Lots of media
represented - and a variety of folk art.