Bab.la has a large number of relatively simple series of exercises that varies by fluency-level. You can access them with or without registering. One nice advantage of registering (which is quick and easy) is that you can very easily create quizzes of your own. Creating these kinds of quizzes, under teacher supervision, could be a nice assignment.
In addition to this kind of language-learning, the site has created a nice map of world languages. They also have a limited number of hard-copy posters of this display that they’re giving away free. You can request one here.
I’ll be adding a link to Bab.la somewhere on my website.