I have used kite nylon. Some of the kite manufacturers sell material so people can design and make kites and some intensely amazing banners. I think I got stuff from Into The Wind years ago (and that stash is lost in the basement mess at the moment).
http://www.intothewind.com/shop/Repa.../3-4-oz._Nylon
and seeing these is why I ordered the rip-stop nylon. I wanted to make some of my own!
http://www.intothewind.com/shop/Wind...gs_and_Banners