The BBC has a number of great Flash-based math games to help introduce or reinforce a concept (or two) on their math focus site.
What's nice about the way the BBC has set this up, is that you can even embed a particular game, review or quiz on your own class site. (The embed code is provided for each activity.) This gives you a little more control over kids being distracted away from the task at hand. And, it means you can point your kids to a practice space on your webpage for at-home review.
(Even older kids might get a kick out of the "cheese-y" graphics!)
