I know in class people were talking about what wire is best for making armatures and what kind of clay is best also. I did some googling and I found a site that appears to be from a UPenn Claymation course. On it, there's links to how to build an armature, and it suggests the type of wire. If you scroll down, it also kind of compares the different types of clay that can be used to make a claymation -- even with price differences. Check it out and some of the links.