There's also insulation foam you can get at hardware stores
My sculpture teacher made some huge, six foot tall, seven foot long anenome looking things out of the stuff. You can cut it with a bread knife and shape it using files. It's a little brittle, but it's lighter than wood and easier to carry around. You can cover it with a glue or a cement to make it stronger, too. That way you can get curves and such.
I've never tried it myself, but I've seen people make awesome stuff out of wood before.
Also, if you need any ideas, go here:
http://www.amethyst-angel.com/cosplay.htmlAmethyst is incredible at cosplay. Her Alphonse elric armor is seven foot tall built around a pair of four inch heels. You've got to give her props for that one.
If you're lucky, her prop blog:
http://proplady.livejournal.com/ , has instructions on how to make certain things like Squall's gunblade, Chronowatch, and Axel's frisbees. Or something.
