There are basically two classes of grant makers - foundations and governments
The category of foundations includes private, family, corporate, and community foundations. Start local: Private donors may already be lurking in your membership; family foundations are often looking to support non-profits within their own locale; and community foundations serve as a clearing house for local private and family funding sources, they also may provide management and training for small non-profit organizations. Corporate support may come either from the corporation directly or through a foundation established by the corporation specifically to fund social causes served by non-profit organizations. Some foundations distribute grants nationwide, so research efforts should eventually reach beyond the local area.
Government funding is available at all levels - municipal, county, state, and federal governments. Particularly at the federal level, the process of applying for a grant can be very labor intensive. However, the federal government also passes some portion of it’s funding down to the local levels thus reducing the amount of red tape in applying for those funds.