I think seanahan is talking about the Samoa cookie that Girl Scouts sell in the US. There's a picture of a Samoa on this page -- it's the chocolate striped cookie in the lower left, above the phrase "Craving Cookies?"
Wikipedia says that Samoas, together with the similar Caramel deLites, account for 19% of Girl Scout cookie sales in the US, making them the second most popular variety (after Thin Mints, of course).
And here I have to agree with seanahan -- Samoas are so tasty as to be downright addictive. With all that caramel and chocolate, they're more like candies than cookies.