There are a variety of external databases where graduate students can seek funding for specific research projects (in addition to fellowship opportunities:

• Federal Grants Database: (Grants.gov). This website is a comprehensive and searchable datbase of all federal research grants. In addition to browsing by category and agency, you can use keyword searches and email alerts to ensure you have up-to-the-minute information about grant opportuniteis relevant to your research.
• Foundation Center (foundationcenter.org). This website offers a database to a variety of private grant-making organizations..
• Community of Science (http://fundingopps.cos.com/about/fundingopps.shtml). The Community of Science is a subscription service available to NETID holders through the university. Their website has a database that includes research funding for graduate students, among others. As its name may suggest, it is primarily useful for those in the social, natural, and applied sciences. More information on services available to  Princeton University students through the Community of Science is available here and here.