We used 2 sheets of transparency film, the kind you use for overhead projectors, which we bought at office max. My son then used a sliding plastic binder from another report cover to bind the front and back together and then we had a clear binder. You can also print from your computer printer on the transparencies to make it your own style. You have to buy the transparency sheets in a group of ten or more though but it is well worth the investment. We also used those to print off photographs for some interesting effects.
Do you want the entire thing clear, or just a front and spine with a clear protector over it into which you can slide your own cover/spine art? I've never seen an entirely clear binder, but you can buy the kind I mentioned at any WalMart.
Personally, I can't shop at Walmart because of their current discriminatory policies, that's just my personal stance. I would recommend Staples, if they don't have something in store that's on their website, they'll have it shipped to the store for free. The entire basics for my business came from Staples. :)