Get a variety of mattresses on sale at the Memorial Day Mattress Sale at Walmart.com. Plus, shipping is free over $50. Some best bets are this Queen 8" Mattress-In-A-Box which drops from $209 to $189 or this Beautyrest Siesta Memory Foam Twin Guest Mattress which drops from $69 to $59 (it's going for $71-$105 everywhere else). Sales tax is charged in most states.