The Howard Hughes Medical Institute has announced open competitions for two programs of particular interest to medical students: "The HHMI Research Training Fellowships for Medical Students Program (Medical Fellows Program)," and the "HHMI-NIH Research Scholars Program (Cloister Program)." See the HHMI web site for submission deadlines and program details.
http://www.hhmi.org/medfellowships
http://www.hhmi.org/cloister