I have been to Dallas in March 2006. People there believe there was 6 shooters, 2 on the Grassy Knoll (left), 2 in the Texas Depository Building (red building on the left on the left), one in the Dallas Tex building (in the dark red building in the center) and one on the roof of a white building (center). Evidences like photographs and prints of bulletts on the ground undertake this theory.
I prefer the Onion theory (paraphrase):
JFK killed by Oswald, Johnson, Communists, CIA, KGB, Congress, Telephone Company and Mob--President Dies in Hail of 35 Bullets from 17 Directions