[Fawn Liebowitz]

Denny's Beer Barrel Pub in Pennsylvania is supposed to have the biggest burger - I realize Wikipedia isn't the most reliable source, but I saw this on one of the late night Travel Channel shows a year or so ago.

It started with a 6-pound burger that contains about 5 pounds of toppings. Patrons take the challenge of trying to finish it in the allocated time. BWMC pharmacist Russell Fortney of Millersville, Maryland,weighing 200 pounds was the first person to successfully finish the 6-pound version.[1]
Soon afterwards the restaurant introduced a bigger burger called the Beer Barrel Belly Buster, a two person challenge. This burger contains a 10.5 pound burger, 25 slices of cheese, a whole head of lettuce, three tomatoes, two onions, 1.5 cups of mayonnaise, relish, ketchup, mustard, and banana peppers all between one enormous hamburger bun. On October 17, 2008, Brad Sciullo, a Pennsylvanian chef, became the first person to eat the burger on his own in under five hours.[2]
On February 24, 2007 Denny introduced a 123 pound burger priced at $379. Besides an 80-pound burger, it contains a pound of lettuce, ketchup, relish, mustard, mayonnaise, 160 slices of cheese, five onions, 12 tomatoes, 2 pounds of banana peppers, 33 pickles, and a 30-pound bun. Denny's goal is to get the latest burger creation into the Guinness Book of World Records.[3]