I recently designed a charm bracelet with ERWMA color "belts", as well as a charm pendant.
I originally used Sculpey III clay (oven hardening) but am not best pleased with this brand. I have used this type of clay before, but the Fimo brand. I believe I'll be going back to it. The Sculpey was hard to work with and brittle, and didn't dry (bake) as firm as I like. I have some Fimo on order and will try again! We'll use the leftover Sculpey for beadmaking.
I've also decided to make smaller "belts" for the pendant.
Articles I found after the fact:
Best Polymer Clay
Makes me mad
Update 12-29-11: I got my Fimo clay in and did some test pieces. It is definitely better than the Sculpey! So I'll make a couple of prototypes and then order more clay for the "production run". I'll also be perusing the online catalog at Fire Mountain Gems to decide on charm holders. It sure helps having a pasta roller to use for the clay rolling and cutting!