For Little Bean's math curriculum we use Right Start Mathematics (Level A). Right Start is a math curriculum designed for homeschoolers, which utilizes the abacus. So far, I couldn't be more pleased with this curriculum. It is intended for children a bit older than Little Bean, but Litte Bean is very bright for his age, and I really couldn't find a pre-k curriculum that was challenging enough for him, so we went with Right Start. Since it is designed for older children, I pick and choose what lessons to present to him and how often/quickly. We play the math games bunches of times before moving on to a new concept, rather than learning several new concepts at once and then reviewing them simultaneously.
What I love about Right Start is that it focuses on learning math through games, thus it is highly interesting to Little Bean. It is also heavy on manipulatives, which I think is so important for children. Right Start emphasizes understanding and true knowledge, versus just memorization of math facts. For example, one of the starting points for students who are using this curriculum is learning to recognize groups of numbers (ie. 5 is all of the blue beads on the abacus, 6 is 5 blue and one yellow or 5 and 1, 10 is two sets of 5, etc.), rather than focusing on counting (which can be tedious and inaccurate), and for that, the abacus is used. Below, Little Bean is completing the bead stair on his abacus (these were taken on separate occasions, hence the change of clothing for him!):