Pulp Avengers is a sourcebook for role playing in the 1930s and 1940s. It’s perfect for providing a realistic background for your games of the Pulp era.
Dirty 30s is a sourcebook for role playing games set in the 1930s. It has a timeline and notes on fashion, slang, prices, jazz, Natiz, Commies, the Mafia, wars, Airships, weapons, cars, ships trains, art, architecture and more.
I like to make my wargaming terrain as authenthic as possible. I found the Chinese Visual Sourcebook to be useful when I was working on my 25mm Boxer Rebellion project.
The Internet Medieval Sourcebook is a fantastic resource for miniature wargamers. I’ve had this one in my bookmarks for several years and haven’t even begun to plumb its depths. The section on the Crusades is particularly useful.