They're really easy to make with shrink plastic/shrinky dink. You can get sheets of it at craft stores. All you do is color your design on it with markers or whatever (or you can buy sheets you can print on from the computer), cut out the shape, punch a hole, and bake it for a few minutes. It shrinks down to a nice plastic tile. Here's one I made a while back:
(a couple others that didn't turn out as well are posted here
Those images you posted are from 4square
and Jewelry by Jessica
, by the way. Always nice to link to the pros, I think.