Grammar in Focus

Road to Grammar with Road to Grammar Junior provide Quizzes on various grammar topics with notes, Extra Extended Practice on major grammar topics with all the necessary information, interesting interactive Games, Downloads both for teachers and students. There is also Road to Grammar blog with more ideas about teaching grammar.

Cambridge English Online where we have recently found the great Phonetic Focus (read here) also offers wonderful Grammar Gremlins - a funny short grammar game with elementary, intermediate and advanced levels. You will have only one minute to complete the five questions correctly. A nice way to master grammar!
The site has other interesting interactive activities: Tower of Babble with matching the question and the answer, Wild West English with various games included, English Doctor with testing on over 70 idioms using body parts and many others.