One of my favorite discoveries in Paris from last year is a shop called Tombées du Camion (roughly, "Fallen off a truck") hidden at the end of a not-very interesting street, on the west side of Montmartre. If you're on your way to the Montmartre Cemetery (to pay hommage at Truffaut's grave, of course) it's a perfect pitstop. A dark little hole in the wall filled with dead-stock French goods dating from the 20's to today. Chanel powder samples from the 40's, dolls heads, gilded Art Nouveau perfume boxes, grade-school report cards, keychains, and things you can't readily recognize are crammed into cubbies, hung from the ceiling and sorted into bins.
Link to numerous flickr photos of the shop