At the Mary Todd Beam workshop, she showed us an easy way to make stamps. All you need is a small section of foam insulation that you can score and break into small pieces. From a craft or dollar store get some of the thin craft foam that has the peel-off backing. You can cut shapes from that and stick on to the pieces of insulation and voila! A stamp!
I used some of these to stamp patterns on some paper to make collage material. I stamped the pattern first and then applied watered down acrylic paint. Fun!