It looks like math teachers are about to become obsolete: Mathway is a website where you can type in problems ranging from basic math to Calculus and not only get the answer, but a step-by-step explanation. All of the key vocabulary words in each explanation are linked to an online glossary. You can graph answers on the coordinate plane when needed as well.
This should be on every students' list of sites to use for homework help, as well as a great self-directed way for students to check their own work. You could do anything from a set of problems, project or test and then have students correct everything themselves and get detailed explanations all from one website. It's fantastic.
There's not much about the people behind this great, free resource, but the company is called Bagatrix, which if I recall correctly was selling software not too long ago that did the same things Mathway does. If this is them reinventing themselves, I think they'll have a bright future.
Originally linked by Larry Ferlazzo, the go-to guy for everything educational on the web.