We’ve written about CSS Zen Garden before, but development of style sheets for that site has really taken off. There are some truly breathtaking designs on display over there. Try these links — any one of them will blow your mind.
fleur de l’avante-garde
Pret-a-Porter (long horizontal scroll on this one; by design)
These designs are so stunning, that it’s worth a recap to explain that the HTML is not changing. Each design just has a different CSS file attached to it.