Early in my second year of grad school, the professor teaching my research seminar course assigned us a report on available grants in our field of study. I can no longer recall if there was a minimum number we had to identify, or what the report required as far as a description of these grants, but it was an incredibly useful exercise for learning where to find funding opportunities. Here are some of my tried-and-true sources for finding calls for proposals (CFPs):
1. AHA Today: The blog of the American Historical Association, for me, has replaced the old method of reading the back pages of Perspectives (the AHA's print publication). This blog does not exclusively publish information on research grants but when an exciting funding opportunity arises the AHA usually publicizes it in a short blog post.
2. H-Net: The best way to describe H-Net is a giant group email (listserv) for humanists and social scientists who study a particular topic. For example, I subscribe to H-Urban and H-Jewish Studies. As a subscriber, I receive occasional email updates about conferences, publications, and grants. There are SO MANY different H-Networks, and thus many different ways to find out about opportunities.
3. Professional Affiliations: In addition to the AHA, there are many smaller professional organizations dedicated to particular historical subjects. As a member of the Association for Jewish Studies I get access to a Grants Directory that lists all of the CFPs related to Jewish history (note: the directory also includes grants for research in other disciplines). Joining a professional organization usually offers the benefit of accessing aggregated or pre-circulated grants in that field of study.
4. Google: With the appropriate search terms, it's possible to find grants you may have otherwise missed. Even after a thorough scouring of the sources listed above, it's valuable to do a general search like "civil war history grants" or "funding for oral history projects." It might turn out to be a duplication of effort or redundant, but who knows--it could turn up a more obscure pot of money.
5. Word of mouth: My advisor has passed on a lot of grants to me over the years, because after 20+ years of scholarship and professing she is on way more email lists than I am. I've also had colleagues pass along opportunities that they thought were a good fit with my research interests. Sometimes those end up being too much of a stretch, but I've applied for several grants that I found that way! It's important to build a strong network, because there aren't enough hours in the day to do research and find all of the various possibilities for how you can fund it. Colleagues help each other out by sharing information.
Any other good suggestions for where to find research money?