Quizlet is a nifty (yes I just used the word nifty) quiz generator that has a surprising range of options for testing your students' knowledge. It is largely designed around the flashcard premise so it really works well with vocabulary words or with facts that need to be memorized but if you browse through the different samples in their library of quizzes you will find that people have found ways to use Quizlet for a variety of subjects and purposes.
Each quiz that you create can be used in different modes that include Familiarize, Learn, Test, Play Scatter and Play Space Race. The last two are simple games that help reinforce the content in the quiz. The best way to learn about these different quiz modes is to watch the demo video they have on the site. You can make your quizzes available to the public or private to only those specific people you choose and you can make them accessible through a direct link or by sending e-mail invites directly from Quizlet. You can take quizzes without an account but if you want to keep track of your progress you need to sign-up, which is free. Having an account also allows you to create groups, for instance for your class, so that you can share quizzes directly with those groups. You could even have students create their own quizzes to be used by their peers.