http://www.ezschool.com/Games/Homophones.html

This one is difficult but great fun : http://homonymgame.com/1.html

http://www.vocabulary.co.il/homophones/

My favourite game so far …

http://www.vocabulary.co.il/homophones/high-school/high-school-homophone-game/

http://www.vocabulary.co.il/synonyms/ (Intermediate synonym game is great).