Mathway - select your subject (algebra, chemistry, geometry, etc.) and enter an equation. It shows you the step-by-step process and answer.
Ultralingua - online bilingual dictionary and verb conjunction site.
Duolingo - free language learning website; just create an account! Available as an app as well for mobile language lessons
Factmonster - general homework help. Offers hundreds of free study guides for various subjects. Easy to use and browse. (Science and history guides as examples)