Please see the following websites to search for funding sources:
-www.grants.gov: Search all federally-funded grant and fellowship opportunities
-www.cos.com: Search both federal and private grant and fellowship opportunities
-www.scangrants.com: another search for funding, categorized by research topic
-www.cdc.gov/od/pgo/funding/FOAs.htm: Centers for Disease Control and Prevention
-http://grants.nih.gov/grants/guide/index.html: National Institutes of Health
-www.samhsa.gov/grants/2009/fy2009.aspx: SAMHSA (Substance Abuse and Mental Health Services Adminstration)
-www.hsrd.research.va.gov: Veteran's Affairs
-www.hrsa.gov/grants/default.htm: Health Resources and Services Administration
How to find out if something's already been funded by the NIH:
CRISP (Computer Retrieval of Information on Scientific Projects): http://crisp.cit.nih.gov/crisp/crisp_query.generate_screen