Here are some links I like, because they rely on clicking rather than typing:
This one is quite hard, but ace for identifying multiples:
This one doesn't have a timer, so it's not so pressured. You can also use it for + - and /
I think this is a basic matching game, but I've got a 'Java virtual machine' error at the moment, and can't try it!
This one is similar:
With this one you have to turn your space station to shoot meteors. Practises factors: