Adding my recommendation for the Neat Sheet. Great product! The fabric repels water and sand, making it very easy to keep clean. The only thing that sticks to mine is sticker-type plant material (think sand-burrs).

One additional comment, the original Neat Sheet product is discontinued, so I believe. They are still available on after-market, such as e-bay, or Amazon, but the marked-up price is tremendous. I paid perhaps $7 at Walgreen's for my original Neat Sheet in 2003 or so.
http://www.amazon.com/The-Neat-Sheet-Ground-Family/dp/B000089SAY

A comparable product is available at Toys R Us or Babies R Us. I have one in my bag now to test later this month on the beach and will let you know how it compares. The price varies by size of sheet. See link.
http://www.toysrus.com/product/index.jsp?productId=18511436&cp=&parentPage=search

Good travels,
Shari