Trackline Magnetic Surveys:
NOAA's Geophysics Trackline Data includes both marine and airborne magnetic surveys.
Satellite Data:
Swarm is a European Space Agency mission for geomagnetic research. A launch blog is available!
CHAllenging Minisatellite Payload is a German small satellite mission for geoscientific and atmospheric research and applications managed by GFZ
Satellite data from the Ørsted Science Data Centre
Defense Meteorological Satellite Program
Observatories:
Holds the Geomagnetic Data Master Catalogue, containing digital minute and hourly mean data
The World Data Center for Geomagnetism housed by the Atmosphere Space Research Division of the Danish Meteorological Institute in Copenhagen
The International Real-time Magnetic Observatory Network is a global network of observatories monitoring the Earth's magnetic field
SuperMAG is a worldwide collaboration of organizations and national agencies that currently operate more than 300 ground based magnetometers.
Crowdsource Data:
A smart phone application developed by NCEI that uses the magnetometer in cell phones to create mobile magnetic observatories.
Geomagnetic Indices:
The World Data Center for Geomagnetism and Space magnetism at Kyoto University DST Index service.
The United States Geological Survey (USGS) Real-time DST service
The GFZ Helmholtz Center Potsdam Kp index service.
The NOAA Space Weather Prediction Center provides a Real-time Kp index service.
The NOAA Space Weather Prediction Center provides a F10.7 index service for the previous 30 days. Older F10.7 index values are available at OMNIWeb Service, LASP and Potsdam.
Paths to Magnetic field, Plasma, Energetic particle data relevant to heliospheric studies and resident at Goddard's Space Physics Data Facility.