I have always been interested in postcards but only became an avid collector in 1997. While I include 22+ categories on my "Postcard Wants" trading lists, I have a special fondness for cards from towns where ancestors lived. As the catastrophes of El Nino have shown us in 1998, landmarks and buildings can vanish without warning. Postcards are a link to the past.
If you, too, are interested in locating postcards that illustrate the history of your family (and maybe, if you're lucky, a family member!) these sites can help:
Playle's Online Auctions
Web-Pac Antiques, Postcards, Autographs, Ephemera, and Collectibles Mall