Six days ago, I discovered freerice.com.
My wife, who has a bigger vocabulary than I have, achieved a perfect vocabulary level of 55 and sent me a screen shot to prove it:

One secret to success is to set up the options to save your score so that you don’t have to start over each time. Another secret to success is to be persistent, because you’ll learn the words you need to achieve a high score.
I haven’t had the time recently to attempt a perfect score, but eventually I’ll get around to trying.
[5-Jul-2008] Five more levels were added in May, 2008, so now the top possible score is 60.
