Have you used bleeding tissue paper before? This idea at Crayon Wishes and Popsicle Dreams was an activity at a Rainbow Art birthday party. The result makes beautiful stand-alone art but could also be used as a layer in multi-media art.
Are you intrigued by the idea of making your own bouncy balls? About.com shows you how to make them with borax, corn starch, and white glue. What a fun way to introduce chemistry to kids!
The Artful Parent has a great post that includes photos and tips of all of their melted bead experiments. At the bottom of her post are links to basic instructions and more. These are made with melted pony-type beads, not melty (Perler, Hama) beads. I think the main concern is the odor and toxicity of the melted beads but this is addressed in her posts along with the recommendation to melt them in a toaster oven outside. I love them all but I think these free-form spirals are my favorite!