Sightings Throughout History
http://www.discovery.com/tv-shows/shark-week/videos/megalodon-monster-shark/This is another video i found through discovery.com talking about not only its sheer size and how it dwarfs the great white but it also talks about how there have been recodings of polynessian fishermen describing in vivid detail of a 100 foot man eating fish. There is no other fish in the sea that fits the description better than C. megalodon.
http://www.discovery.com/tv-shows/shark-week/videos/megalodon-monster-shark/