I recently found a blog by an artist living in Mexico, Geninne Zlatkis, who, among other things, makes wonderful hand-carved stamps. She wrote a book about how to do it too, Making An Impression: Designing and Creating Artful Stamps, which I got for Christmas. Here are a few photos of some stamps I carved recently.
Moo Carve which is easy to cut and good at not crumbling. (I had used a different product before which wasn't bad, but this stuff is better.)