While touring preschools, I noticed my DS3 quickly gravitated to a container of Unifix cubes. I later purchased them along with a 1-10 stair, and it's amazing the number of ways he has used them - one time they were seeds that he planted, another time fruit salad, trains, etc. He also uses them to create patterns, and I recently observed him constructing math facts for 10 with the stair and happily talking to himself about "all the ways I can make 10". They are different from the Cuisenaire Rods you are considering, but you might find them of interest.
