Here’s a great resource if you are writing or drawing anything from the beginning of photography through the 1940s. Shorpy’s is donated copyright free images from the dawn of photography. Not only is an amazingly inspirational thing to add to your RSS feed, but there is also lively discussion of the images. If you have some to add to the pool, they’re always looking for new stuff.
You can even check out the history of cat photography! It existed long before the internet.
Also, I’ve blogged this site before, but their content, scans of copyright free beautiful books, is amazing – Bibliodyssey. They just posted a group of pre-printed envelopes from the Civil War that are worth a look.