Both SPIN and SMARTS can be used to search for fellowship opportunities.  In addition, the following resources are available for identifying different types of fellowships:

Making the Right Moves: A Practical Guide to Scientific Management for Postdocs and New Faculty: http://www.hhmi.org/resources/labmanagement/moves.html

The F Kiosk: Individual Fellowships at NIH: http://grants.nih.gov/training/F_files_nrsa.htm

NSF: Find Funding tool: http://www.nsf.gov/funding/

National Center for Environmental Research Fellowships: http://es.epa.gov/ncer/fellow/

American Society for Engineering Education: http://www.asee.org/fellowships/index.cfm

The Life Sciences Research Foundation: http://www.lsrf.org/pages/geninfo.htm

The Leukemia & Lymphoma Society, Career Development Program: http://www.leukemia-lymphoma.org/all_page?item_id=11618