Today is National Hamburger Day and that means beefy deals! Several burger joints are offering specials, including Burger King, where Royal Perks program members get a free hamburger with a $3 purchase. Shake Shack is offering something similar, but the minimum buy in is $10. Dairy Queen is offering a dollar off its Signature Stackburger for the entire week. Other deals are available at chains like Sonic, Whataburger, Smashburger, Jack In The Box, Red Robin, and Checkers.