Here are a couple of fun math websites.

http://www.funbrain.com/
Fun Brain is a great all around website that has many games for all skill levels.

http://www.coolmath-games.com/
Cool math in general is a great resource for students who struggle with Math. Cool math has a variety of games that help with specific problems student might face while doing Math.

http://funschool.kaboose.com/arcade/math/
Just another great website.