Math is fun. Learning arithmetic sometimes isn't. One way to make it more fun is to understand the point of math.
My oldest (12 at the moment) is using Math-U-See to learn and practice computation. Math-U-See is great for that. We also use Life of Fred for more of an over view of the subject, but it still doesn't help understand the real fun and beauty of mathematics. That's where these books can come in.
Here are a few books by Isaac Asimov about math that my then 11 year old enjoyed reading.
Realm of Numbers
Realm of Algebra
Asimov on Numbers
For more books and ideas to help discover math check out the reading lists at Living Math too.
Also, just recently recommended to me was the essay "Piece of Pi" in the book "Adding a Dimension", I'll try to remember to post about it when it comes in from the library.
Read any good math books recently?