I was talking to a physicist friend who was quite happy to hear about how much my son Neal loves science. I asked my friend about what was important to get across to a science-minded child, and he said, "Math. How far he succeeds in math will determine how far he can go in most areas of science."
He then went on to say that what's important isn't knowing the times tables extremely well, though that doesn't hurt, but knowing how to actually use all the numbers to solve real-world problems. It helps to see the beauty and the power of mathematics.
This lead me to devise a much more friendly approach, aimed at helping kids to be more likely to enjoy math, to appreciate what they can do with it, rather than to see it as endless lists of computations.
The computational side must be dealt with, of course, but for most children this can be made more enjoyable and more effective by using games. Children's minds tend to hold on to things that they've actually used much better than ones that they memorize for a test....and 'use' seems to include Math Blaster and multiplication war card games!
In practical terms, this means that we follow a regular mathematics curriculum with a few twists. Currently we're using Sra Math Explorations and Applications, which is an older series that is very highly-rated by mathematicians and scientists, as well as by my children. We love the emphasis on real-life problems and situations, and the use of games for drill. We do most of our work on memorizing the four basic operations using games, whether cards, computer or activities. (We do a few written pages here and there to document it all for our year-end portfolios as required by the State of Ohio.) We do much of the story-problem work out loud, with scratch paper available for computation. We supplement this all with extra thought problems from the Challenge Math series, and the Critical Thinking books from Prufrock Press.
Another fun source of mathematical enrichment and amusement is puzzle books, like Sudoku, kakuro, logic problems, and other mathematical puzzles. These can keep an older child occupied for hours. Highlights has a series called Mathmania, which is very good for younger (5-10 year old) kids.
Sometime around age 12 or beyond, Jacob's Mathematics: A Human Endeavor can be an excellent text or supplement to any curriculum. It introduces many of the great mental puzzles and challenges of more advanced math, but at a level that can be appreciated by most people. It brings out the beauty and fascination of math.