This flickr group, Looking into the Past, is too cool. People find these old photos of recognizable locations, and hold them up in front of the modern day scene.
Of course there are books that do things like this, overlaying the old and new (my dad gave me one for Christmas a few years ago about New York and it's so cool), but I love that this one is just random people recognizing places they know in old photographs and contributing to the project.
It makes it a little more personal-- you wonder how they found the photo, or what association they have with the place or the buildings that used to be there. Did thier grandparent work in the building that was there? Do they live near this spot now and they wondered what used to be there and looked it up?
Definitely provokes some wonderment...
flickr set here
found via Swiss Miss