Historypin is an extremely cool, user-generated archive of historical photos and stories. The website combines Google Maps with photos and stories uploaded by the public to act as a virtual time machine. You can even use Streetview to take a tour of places with historic images overlaid.
The site is relatively new, so some areas are lacking for photos, but it's worth a look. You might even want to help the cause by uploading some of your own photos or stories.
[update]
Historypin is currently featuring several Clay County Historic Sites photos. Head over to their twitter feed to see links and some kind words!
Thanks to Emily Doolan for adding so many great photos to the site.