National Science Foundation - Research Experience for Undergraduates (REU) List of REU Summer Research Opportunities https://www.nsf.gov/crssprgm/reu/reu_search.jsp (Deadlines in January, a few through March/April)
NASA Internships and Fellowships https://intern.nasa.gov/ossi/web/public/main/ (Deadline early March)
NIH National Institute of Health Summer Internship Program (SIP) for Biomedical Science https://www.training.nih.gov/programs/sip​ (Deadline: March 1)
William Randolph Hearst Minority Fellowship Summer Program https://aspeninstitute.wufoo.com/forms/2017-william-randolph-hearst-endowed-fellowship/ (Deadline: March 17)
National Science Foundation Graduate Research Fellowships Program (NSFGRFP)- open to undergraduates intending to pursue graduate school in an NSF-sponsored STEM field. https://www.nsfgrfp.org/
Barry Goldwater Scholarships https://goldwater.scholarsapply.org/
Cambridge - Gates Fellowship https://www.gatescambridge.org/