There are a bunch of handy sites out there with materials that you can use in your classes. Please contact the site if any of these links break!
Japan's premiere clip art site. All pictures are 100% free, but you'll need to search in Japanese.
This site takes recent world news articles and generates exercises based on them. Useful for students high school age or older.
Make your own Jeopardy quizzes in a web browser. You can set the number of teams or download your quizzes for offline use.