From the good people at the balance board blog.
What appears to be the first third party (i.e. not official) Balance Board imitator has now popped up on Amazon's listings, and it's from a firm called Njoy.
Christined the G-Board Balance Board and priced at £64.99, it sports a number of differences to Nintendo's original creation. As well as markers for your feet and a crosshair that divides the board's surface area into four separate zones (handy for the likes of the upcoming Skate It, no doubt), there's also an LCD display, which looks like it'll show your weight when you stand on it.