Grants for graduate study often are tied to subject matter. The American Society of Microbiology Minority Fellowships is one source. Look at professional societies in your field for grant opportunities.
Minorities may find many grant opportunities like the American Indian Graduate Center Fellowships, Cornell University Graduate School Fellowships for Minorities and others.
Check with national fraternities and sororities to see what grants they offer.
Education majors willing to work in high-need areas may qualify for grants. The University of Phoenix offers such grants to adults seeking online degrees.
Doctoral students have many grants tied to research available. The federal Department of Veterans Affairs and Department of Housing and Urban Development offer many of these grants.
Universities and colleges with postgraduate programs will offer grants and fellowships to their students from either the college itself or special endowments.