A great site that has addition, subtraction, multiplication and division games on. The class loves to play these games at school, especially Minko's Milkshake Parlor, Lucy's Costume Closet, Murb and Colour Your Vacation.
Sheppard Software
Has a wide range of games at various levels. Scroll down to the fractions games, we've been playing these in class this term.
BBC Bitesize
Another site with a great range of games. In class we play number ordering, number sequences, addition and subtraction and multiplication.
BBC Starship Maths: Park the Pods
A fantastic game to help with number ordering, counting on and even skip counting.