A great English game where players shoot the correct word when given the word class, such as noun, verb, adjective etc.
http://ictmagic.wikispaces.com/English
I have just uploaded a couple of videos onto youtube going through some German grammar. At the moment I have done accusative and dative pronouns and adjective endings following indefinite articles.
This site teaches grammar through a good collection of multiple choice quizzes and games. There is also a junior version of the site for younger learners. Both sites also have downloads for teachers.
http://ictmagic.wikispaces.com/English