We used Building Thinking Skills, but it was a long LONG time ago, and we used a science concept map book that I think is now out of print... Both of them were cute and fun and I liked them, but we were done with them extremely quickly, and much younger than suggested... Which is not to say they're badly aimed or anything, just to trust your own knowledge of your own kid in choosing levels. There's nothing magic about the suggested age ranges.
More recently we've used books from their Critical Thinking in U.S. History series, which I really liked. I think that one has been my favorite, because it took the topics we were already reading about and beefed up the discussion significantly, plus addressed the aspect of history that I find most important - that history is written from a point of view, and not as a dispassionate list of Facts. It was also an excellent resource just for the variety of sources it quoted. Whether you were using the exercises or not, it was a useful thing to have six different takes on the Roanoake story, for instance.
