Education

has a math program called "Investigations." I taught it for several years before I moved into middle school and stopped teaching math. As one of those students who "hated math," I was looking for something that made more sense; that I could bring to students with a sense of curiosity and confidence. It's inquiry-based, all about concepts. Its also really powerful. In the years I taught it, I never had a math-hater, and most students left me well above "grade level."

It comes with a teacher's manual; that's it. At least, it did 12 years ago. It required manipulatives and a copy machine. There may be more to it by now.

More info: http://investigations.terc.edu/