Someone pointed this site out to me, and it's quite fun. If you want to improve your vocabulary and at the same time donate some rice to those who need it, go here: FreeRice
It will give you a multiple-choice set of answers for a word's definition. The site sets a vocabulary level for you based on how you do with the first few words. The highest level is 50, but apparently anything above 48 is very rare.
I learnt a few new words that I had never even heard of before. Of course I can't give examples, because I've already forgotten them....but hey, it was fun and in a good cause :-)