Walmart's Mattress Sale Includes Tons Of Options For Under $400-All The Way Up To A King

President's Day and mattresses might not seem like a pairing as classic as peanut butter and jelly or three day weekends and snooze buttons. But this time of year actually sees a ton of mattresses flying off the shelves. (Metaphorically speaking, of course-we don't imagine any queen-sized beds moving that fast.) The simple reason? Sales, naturally. While pricing, discounts, and timing varies from retailer to retailer, one sale is already up and caught our eye. Walmart is offering discounts on so...