You could try Khan's academy, it is very cool IMHO. http://www.khanacademy.org/index.html#Pre-algebra

For teaching materials, try cnx

http://cnx.org/content/col10615/latest/

I would try out something in the LOGO philosophy also (scratch, etoys and so forth). The web is flowing with rich material, so get a shovel and dig up.

I Hope you find some gems.