I have written these quizzes as a tool that my students can use to help them with their studying. It may be that more will follow, if they find them helpful.
Terence Tao wrote some online quizzes that I recommend. (He wrote about his views on such quizzes on his blog.) A lot of these quizzes are relevant to Oxford first-year students. Just ignore any questions/quizzes with words you don't recognise!
NRICH has an Interactive Workout if you want to brush up on your A level skills. It's important to be fluent with these things!
This page last updated on 11th December 2014.