The National Geophysical Data Center (NGDC) is a part of the US Department of Commerce (USDOC), National Oceanic & Atmospheric Administration (NOAA), National Environmental Satellite, Data and Information Service (NESDIS). It hosts several World Data Centers (WDCs) which can be accessed from this site including: glaciology, marine geology and geophysics, solar-terrestrial physics and solid earth geophysics. There's also a link to data catalogue of downloadable datasets on a variety of topics including hazards, marine, satellite, snow & ice, solar-terrestrial in addition to an online data access systesm and an interactive map service. The NGDC also provides links to UK mirror data site.
Freely available data on internet.