www.Grants.gov - This is the US government's official site to find grants it is offering. Remember most grants are for nonprofits serving the public good. However if you are a for profit business you may be able to partner with a nonprofit to help your community.
www.FDNcenter.org - This is the Foundation Center and is where the grant writing professionals go to get legitimate grant sources.
www.fundsnetservices - Another great website to locate legitimate grant opportunities. Used a lot by professional grant writers.