Flashcard Stash provides an innovative flashcard based study tool that is built on top of a dictionary. The makes it easier to create flashcards using dictionary definitions. The site has a number of features, such as engaging games, the ability to add images to flashcards, and a spaced repetition algorithm that tells you when to study.
Create your own list of vocabulary words or use those already available on the site. These include several foreign languages and SAT test prep.