Not a curriculum, but since someone mentioned Cuisinaire rods, I'd also like to mention Base Ten Blocks, which have become a "thing" in math manipulatives. They're crazy useful, AND, although you can buy really nice wooden ones, I got given a set of smaller-sized cheap-o foam ones that are the identical dimensions as Cuisinaire rods. Multiplied awesomeness. We keep our cusinaire rods and base ten blocks jumbled together in one box for maximum cross-over usefulness.