Favorite dog toy:
tail chaser
take a simple piece of rag or cloth, tie it around your dogs tail and voila, they'll be chasing their own tail for hours!
Editor's note: A simple homemade dog toy indeed, although some people may view this as cruel... If it looks like the dog IS having fun and not getting hurt by the rag pulling too tight or by biting him/herself accidentally or getting hurt by bumping into things, then go ahead. Just supervise closely.
If your dog seems annoyed by having something tied on their tail, then we suggest you take the cloth off and try another toy idea instead.