One of the most underrated, and almost forgotten, design elements in the home is the shower curtain. I understand that the function of it is to provide privacy and prevent water splashing out of the shower, but really, how is a shower curtain any different that any other curtain in our homes? Isn't it one of the first things you notice when you enter someone's bathroom? Anyway, if you want to create a truly fabulous bathroom, or just spruce up the one that you already have... start with the curtain and work from there. Wouldn't it be easier to find an awesome curtain and then accessories and towels to go with it than the other way around?
Another tip: Hang the curtain as high as possible... even to the ceiling. It looks much more glamorous and sophisticated that way. If you need to you can always sew a lining into the back side of the curtain or just hand a second rod for the liner (it won't be visible when the curtain is closed anyway)
Also, don't limit yourself to only "shower curtains" when you are shopping. Any curtain, or even custom drapery, can be used in the bathroom. After all, thats what lining is for... to protect the curtain from water damage.
This one is my favorite :)