Serving as a peer reviewer for grants is a significant way to improve your grantsmanship.  Below are some Federal Agencies that need reviewers.  If you don't see the agency you need, please review the agency's website.

National Endowment for the Humanities

National Science Foundation

USDA National Institute of Food and Agriculture

USDA National Sustainable Agriculture Coalition

US Department of Education

Institute of Museum and Library Services

US Department of Health and Human Services

National Community Services

Office of Justice Programs

US Department of Labor