Google Sky Viewer
The sky viewer gadget is useful for visualizing data sets associated with locations on the sky. Panning the viewing window sends the celestial boundaries to the Data Inquirer, which can then be used to construct a data set.
Whenever a new data set is created, the sky viewer automatically searches for an RA and DEC field in the data set. If it finds one, circles are overlayed on the points on the sky corresponding to the data points. Mousing over the points displays a tool tip with all of the fields and values associated with that point.