Count On - a wide range of maths games, puzzles and investigations. These cover a wide range of mathematical areas and you can even learn interesting facts about lots of different numbers.
Nrich - packed with maths investigations and activities.
Digger and the Gang - from BBC Schools website. A range of maths activities.
Number Time - from BBC Schools website. Activities for Years 1 and 2.
Bitesize - from BBC Schools website. KS2 revision activities.
Starship - from BBC Schools website. Help with KS1 National Tests.
CBeebies - activities from all the CBeebies characters, suitable for children up to 6 years old.