You may have tried the Sporke site with its extensive collection of timed quizzes.
There are several mathematics quizzes available. It is also possible to create your own quizzes, give the link to your friends and see how they do!
Can you give all the missing prime numbers in 2 minutes or less?
Can you square the numbers from 1 to 25 in 2 minutes or square the numbers from 1 to 50 in 4 minutes?!
Can you get the correct answers to 60 simple calculations in 1 minute? A mistake will end the quiz.