If you don't think that education or vocabulary can be fun, then try Knoword. It is a fun, fast-paced game that tests your knowledge of vocabulary. And since your answers aren't spell-checked, spelling is tested also.
The rules of the game are simple. You are given a dictionary definition and the first letter of the word and you must type in the rest, while a timer is going. You keep going until you miss or skip a certain number of words or time runs out. It is incredibly addicting, but so educational, you won't care.