Those which have natural ties to your organization or your program. Matching mission or goals. Look first to those that are located in your state, then to national foundations that have very narrow interests which include a close fit to your program or project. Be alert for key words or phrases in the foundation's stated purpose and statement of limitations.
Many nonprofits receive their first grant from their local community foundation.
These are in fact grantmaking public charities, themselves supported by grants and contributions. They serve as a conduit for donors who may not have the resources or the desire to start a foundation of their own, but who still want their grantmaking to be professionally managed. The key point for grantseekers to keep in mind is that community foundations only support agencies or organizations in a specific locale. You won't get funding from the New York Community Trust if your agency is located in Vermont. Get to know your local community foundation.