I realized that I haven't written about one of our favorite math resources--the Murderous Maths series, developed in England and available in the US from Fun Books. The various books tackle different math topics, but in a humorous and applied way. Most of the problems are evolved from a situation or story discussed in the book. Plus they use that wonderful British sense of humor, which goes over really well with my son.
To give you some idea of how fun these books can be, here are some of the titles:
Murderous Maths: The Mean and Vulgar Bits (fractions, percentages, and averages)
Do You Feel Lucky? (probability)
The Phantom X (algebra)
Savage Shapes (geometry)
They are inexpensive paperback books with some cute illustrations, but pretty text dense. However, my son will just pick one up and read it for pleasure--which is saying something for the books, since math is not necessarily his favorite subject. They are not a traditional curriculum, but if your children like stories (and what child doesn't?), they are a nice supplement to the other math you may be doing.
To see a list of the math content in each book, click here.