The manufacturer's suggested retail price of US$19.99 is a small price to pay for the form-fitting silicone cover. As far as we know, it's the only protector available so far for the rMBP. It's black, silicone and matches the function keys printed on the full-sized keyboard's 78 (U.S.) keys.
The NuGuard Keyboard cover boasts a smooth surface that's amendable to fast typing. The form-fitting sheet is molded to cover each key and the space between each key for protection against key wear, food/drink spills, and dust/hair clogging. It's also translucent so the backlit keyboard remains clearly illuminated in low light conditions.
The NuGuard is a little tricky to place on the rMBP. However, it's easy to peel off so you can clean your rMBP. Just remove it, rinse under water, and let it dry before reapplying it. For more info go to http://www.newertech.com/products/laptopAccessories.php.