Check out these UK sites!
Math Starters of the Day
There are 366 different Starters of The Day on this website. These are activities designed for pupils to work on at the beginning of their math lesson. You can search the archive.
Here are a few more sites:
Mr Gallinagh’s Maths Starters - a program of 10 questions for any topic you like. You can specify how much time you give for each of the questions. Can also be used as a test at the end of a lesson to find out how much pupils have learned.
Super Maths World - some of the games are for free. Others you need to be registered to use.
I love Maths Games - puzzles, games and starters.
Calculator Activites - 15 short problems and games designed to make use of a calculator. Ideal for lesson starters.