I'd love to see more collars. I'd like sculpted ones if that were possible, like a sculpted pearls "necklace" (I have one kitty who really wants pearls) and maybe a spiked collar for my tough kitty (right now he has the black one with gems but he wants something a little tougher). Hehe I think they could express their personalities better then.
They could also have brighter designs like these:
http://olivegreendog.com/cocktail-dog-collar.html
I love the RFL collars. Maybe something similar but with a few options for what the collar would say.
I'd be excited to see any new designs that come out.