I am going to test this site with students this week - I have created a measurement challenge game. It is a fun site to use and I think students would like the game approach used. There are some free games and quizzes available but you can also select your favourite questions and write your own questions to create a new challenge.
A large collection of lesson ideas for maths/ science related topics. Choose the 'Search by topic' option at the top RHS to find resources for a topic you are studying.