Ben Millam has built a cat feeder that releases food upon recognition of RFID-tagged plastic balls.
Millam places the balls around the house and his cat, Monkey, has to find them and return them to a bowl fitted on top of the food feeder. When the balls rolls down the chute, instant kitty chow dispenser!
More on training the cat and how to build an Arduino-based triggering mechanism for the dispenser here.
This would be beyond awesome for a dog, though I think the food would have to come down a PVC pipe chute to prevent the dog from taking "direct action" to the Super Feeder.