FreeRice is a non-profit website run by the United Nations World Food Program. You and your students can select an area to be quizzed on, and for each correct answer 10 grains of rice are donated to fight hunger.
You can take vocabulary quizzes in English, Spanish, French, Italian, and German. There are also geography quizzes (flags, capitals, and maps) and one with famous paintings.
Free Rice is available at http://freerice.com