http://en.wikipedia.org/wiki/Polymer 

http://www.pslc.ws/macrog/kidsmac/wiap.htm 

 

And here is Fimo:

http://en.wikipedia.org/wiki/Fimo 

 

See what you can do with Fimo:

http://www.polymerclaycentral.com/ 

 

Below is the one I use.

A very convenient shape, reasonable price and a wide range of colors...