Our dog loves the Molecuball - it looks like 4 little balls stuck together, with a hole in one of them. You pour the treats in the hole, and then the dog has to shove it around trying to get the treats out of the ball. It's a lot easier than the Buster Cube, especially on wood floors.
Her favorite "toy," though, is an old rag with treats in it, tied in knots. She has to pull the knots apart to get at the treats. She'll work at that thing for hours, and it's fun to play tug with it, too. Dogs love dissecting stuff!
