The best i could find are some led ping pong balls. In greg’s new video he is using POI leds balls for tracking as i was skimming through replies of comments. I have actually bought them but they are not the official ones to buy. Greg said in the comments that he is looking for a person who could make some smaller ones as they were a bit too big for what he said. I can see that he just used a standard ping pong led ball for hip tracking as it is smaller. Unfortunately i cannot find ones for cheap and they all require minimal diy skills such as having adhesive velcro straps or a strap to wear around your foot. But hopefully Greg can find ones that are the best for tracking for kinect.