In past few months, I linked to two collections of color photos of Paris taken in the 1910s and 1920s under the direction of Albert Kahn.
Recently Rue89 sent photographer Audrey Cerdan to recapture some of those old scenes in modern day Paris and knocked up an interface so that you can slide back and forth between the old and current photos. In some of the pairs of photos, pharmacies, tabacs, and boulangeries are in the same places. (thx, christophe)