Saxon Math
I have friends who have used Saxon for years and are very, very happy with it. Saxon's circular pattern and constant review is exactly what they love about it. However, it was this circular pattern that caused problems for us. The way Saxon works (someone please correct me if I'm off base here) is that it introduces a new concept in increments, the child works a set of problems that teach a new concept, then spends the rest of the lesson reviewing previously learned concepts.