Khan Academy - Cosmology & Astronomy: This site provides an extensive interactive video library, a community for questions and answers, a large bank of practice questions, and many more resources to help you to succeed in chemistry.
Physical Reference Data: A series of online databases hosted by NIST containing physical constants, spectroscopy data, X-ray and gamma-ray data and more
SciServer: Tutorial on parameter files, fits files, and using bitmasks, and a page with conversions between our wavelength and magnitude systems and other systems.
