American Geophysical Union (students can join for $7 and receive EOS weekly, Physics Today monthly, and great book discounts; regular people (not students) can join for only $20)
Global Earth data sets including topography, earthquake data, gravity, plate motions,
seafloor ages, volcanism data, sediment thickness, world stress map, and seismic hazard; list and links compiled by Thorsten Becker at
Harvard University