I have this weird fascination with looking through old postcards whenever I go in an antiques shop. I like postcards that have actual messages on them and were sent. You'd be surprised how many antique stores have vintage postcards you can weed through and read. It's interesting to read about people's travels and thoughts about a place from 1967, 1985, etc.
The other day I came across these vintage photos for sale on eBay. These illustrate my favorite thing about photography -- moments frozen in time; capturing joy, sadness (look at that baby!), being fabulous, life.