I stumbled upon this site today and thought I'd share. It has a ton of great old images. I especially like the WWII-era photos in color. Anyway, I know there are some here that can appreciate them so here's the site.
Shorpy | The 100-Year-Old Photo Blog

A few samples (higer-res versions available on the site):



Washington Monument


The hanging of the Lincoln assasination conspirators:


US Capital Dome - 1863