Furbies were cute toys that completely swamped the market just a few years ago - with an apparent "personality" and cute learned behaviour.
They were of course Furry (hence the name), and had moving eyes, mouth and ears. They would make baby noises, and progress through acquiring english "vocabulary". This learning was actually just a pre-programmed behaviour.
They had a small Infra Red communicator between the eyes and could communicate- synchronising actions with other Furbies in much the same way the Pino Toy could. They had sound, light, touch and tilt sensors. They also have a motor speed/position sensor.
What is interesting is for all their apparent Degrees Of Freedom they actually only had one motor, and it was through an ingenious arrangement of cams that they could perform so many expressions.
There are a number of articals on hacking and opening these up over the internet.
They can be modded in a number of ways. If you alter their cams - you can change their actions somewhat- though this may just mess them up. You can also get a cool effect by skinning them. I have seen at least one "Terminator?" furby - skinned, and replaced with a leather jacket and given dark shades.
Unfortunately they are not really a platform for doing anything more clever than this, but performing a Furby autopsy is a great way to gain an insight into getting more from a single motor mechanism.