Kitty Ware is the inventor,of the Greta Scrambler. It looks like a giant egg, and is made of hard plastic, that comes in various colors. Dogs can herd it with their front feet, and can't seem to get a grip on it. It's always just a tiny bit away from being caught. We have had to limit play time for our dog to 15 minutes a day, because she was getting too wild and hurt her leg. At this time I can't find a place to buy it, but will update this when I get more info.
Here are some pictures of the EGG and dogs playing together

http://www.colliecapers.com/gallery/more_eggfun

Pros: Dogs go crazy for this toy

Cons: Hard to find/buy. Limit play time,...Dogs go crazy for this toy