Here's a fun website where you can view "Penny Postcards" (postcards from the early 1900's that cost $.01 to send) from your state...maybe even your own hometown. There's only one from mine - Tabor, SD. It is and always has been a pretty small town. Here's what the main street looked like in the early 20th century...
Obviously, the bigger the city, the more postcards you'll find. This could be fun to use in some heritage scrapping.