I stumbled upon PopSpots by Bob Egan today, and I couldn't stop checking out his work. He tracks down the exact location where famous events in pop culture have happened, photographs the location, and overlays the historical photo.
Some of my favorites...
The Who's "The Kids are Alright" album cover
West Side Story album cover
Neil Young's "After the Goldrush" album cover
My Name is New York by Nora Guthrie and the Woodie Guthrie archives