I am currently working on the Menoth half of the two-player battle box. I saw a post from PG_Jolly Angus on how to make mosaic tile bases. This is my first attempt at working with any sort of sculpting putty, but I think it went pretty well. Sorry for the crappy cell pictures, but I was too pumped that I actually finished molding a few bases not to share.
Some of the squares ended up a little more rounded out and the edges aren't as even as I'd like. But I think they'll look great painted up. They'll have a "worn-down" kind of effect that I'll try to bring out with paint.
PG_Jolly Angus's How-To guide: