Virtual Astronomical ObservatoryThe Virtual Observatory (VO) is an international effort to bring a large-scale electronic integration of astronomy data, tools, and services to the global community. The Virtual Astronomical Observatory (VAO) is the U.S. NSF- and NASA-funded VO effort that seeks to put efficient astronomical tools in the hands of U.S. astronomers, students, educators, and public outreach leaders. These tools will make use of data collected by the most powerful telescopes in the world.
The VAO has a comprehensive step-by-step help guide for using their "Data Discovery Tool" to search for data sets. Be sure to check it out before you try conducting a search.