Click here to visit the official website. Confession - we built our own. It uses a little more duct-tape and prayer to hold it together than the official set, but we put it together for a little less than $200. If you've got the budget though, I'd definitely go with the official set.
It really is a lot of fun, anyone can play (it requires very little skill), and kids actually invite their friends just to play it!
Do you have any games/activities that bring kids out like Nine-Square has for us?