I am completely enamored by old photographs. So, you can imagine my delight when I stumbled across The Commons on flickr thanks to Amanda of Peony::Love. I literally placed my hand over my mouth and let out a squeal.
Essentially, the project has two objectives; to increase access to publicly-held photography collections, and to provide a way for the general public to contribute information and knowledge. It is a huge public photography archive. I suggest you pour yourself a glass of wine and get to searching, there are so many brilliant photos to be discovered.