It is said that people changed their view of their existence when they looked at the first pictures taken of Earth (from space or from the Moon).
One thing that has made an impact on me is the following video from TED. I have been interested in Dark Matter since I visited Soudan, Minnesota, USA. The thing that really blew my mind was the number of Galaxies that exists.
George Smoot looks into the farthest reaches of space to the oldest objects in the known universe: fluctuations in the remnants of creation.