In addition to NIH, the United States government provides support for graduate trainees through NSF and the Department of Defense.
Department of Defense
National Defense Science and Engineering Graduate Fellowship
This program targets students pursuing doctoral degrees in a wide range of science and engineering areas, but includes a program in biosciences and a program in cognitive, neural and behavioral sciences. Applicants to this program must be early in their graduate training and have completed no more than one year of graduate work. More information can be found on the DOD website.
The DOD often announces more targeted fellowship opportunities during each federal fiscal year. Many of these are focused on cancer research-related problems, but other areas are also covered. Not all programs provide predoctoral fellowship support. Please visit their website for additional information.
National Science Foundation
Graduate Research Fellowship Program
This program supports graduate students training in areas related to the mission of NSF including biology, technology, engineering and mathematics. The site also offers application tips and advice on the application process. More information can be found on the NSF website.