Quizlet

Quizlet was founded in 2005 by 15-year-old Andrew Sutherland for a high-school French class. He wanted an easy-to-use tool for learning vocabulary. He built Quizlet for himself, shared it with his friends, and it grew from there.

Quizlet is now among the largest educational websites in the world. Millions of teachers and students use it. 

As a memorization tool, Quizlet lets registered users create "sets" of terms customized for their own needs. These sets of terms can then be studied under several study modes.

http://quizlet.com/

For teachers: http://quizlet.com/teachers