One of my favorite discoveries has been Professor B Math. Professor Everard Barret has developed a Math program that uses the natural ability of a child to understand a story as the vehicle for learning and more importantly understanding mathematics. The verbal explanations in this curriculum are crystal clear and children pick it up very quickly. A preschooler can begin the program and a kindergartner can learn addition and subtraction and you will find your student advancing quickly without really trying that hard. We have used the program since the beginning and it has worked wonderfully. Prof B Math is also fun because it is done on the computer both my kids enjoy that aspect. I believe you can buy it in book form also.
The website is very informative and gives the history of the program as well as the philosophy behind it. Several school years are combined into each level that you buy so the price is affordable.
We tend to combine Professor B Math with Saxon at our house. I like to use Professor B to learn a concept and then the Saxon workbook pages as a confidence builder. The only difficulty I have found with doing that is we tend to get so far ahead of the Saxon in ablility I end up buying the next Saxon level sooner than I expected.
You can find Professor B Math at www.profb.com