Magnet Wall! When we were in Arizona a little while ago we went to a children's museum. One of the rooms had a magnet wall with a variety of PVC pipes in various shapes and sizes that you connected and could roll balls down. A larger than life marble game, if you will, that the kids had a blast with. I have been wanting to make one ever since, but Rose said I had to finish the basement first... done mostly ;)!
So with the help of my Dad we got it up yesterday! We still need to make the tracks but the kids are having fun with it still in the meantime.