The SOHO Archive
Allows searches from the sources involved in this ESA - NASA project by setting observation period, wavelength, coordinates, objects and instrument.
http://sohowww.nascom.nasa.gov/data/

Solar UV Atlas from HRTS
A brief presentation of its features.
http://umbra.nascom.nasa.gov/uv_atlas/atlas.html

Solar Data Analysis Center
Features links to data resources. Also includes images, news, eclipse information. Based at NASA Goddard Space Flight Center in Greenbelt, Md.
http://umbra.nascom.nasa.gov/sdac.html

Solar Influence Data Center
RWC Brussels World Data Center for the Sunspot Index. Features archives, forecasts and information.
http://sidc.oma.be/