Free Rice is such an amazing website that I've known for ages. It allows you to play this little word game that not only helps you expand your vocabulary, you also help give 10 grains of rice to the World Food Programme for each correct answer. Isn't that awesome?
A lot has changed since I first saw the website, you can now sign up and join groups. Or just continue to play anonymously. Also there are different subjects you can choose now, such as literature or geography.