Here's a company I'd would dearly love to start ordering titles from. Avalanche Press has a ton of good stuff. Some inexpensive, some a little pricey, but seemingly thorough treatments of the events they represent.
I'm very interested in the WW1 naval titles in their selection. The good thing about Avalanche Press is that they specialize in a period and have a representative game system they expound on, unlike Avalon Hill/SPI which tended to cover as much history as they could, with as many game systems as they could publish.