re: NeilV - Braitenberg "Vehicles" book - enough goodness cannot be said about that book. It seems deceptively simple but its a wonderful place to start thinking about and being inspired to building simple beasties.
As should Grey walter's wonderful tortoise: http://www.bristol.ac.uk/news/2008/212017945378.html
That was two companies ago, AFAIK
Edit: And, indeed, TFA says as much.
I even asked Rodney Brooks whether the results of this paper were applied on some robot platform as a follow up research and received a very interesting reply . I agree that I might have worded it poorly but it's still one of my favourite tweets.
P.S. I posted this comment in reply to a Brooks reference a few days back, but might be more on topic here.
Before you get into that, it's delightful to start with the Braitenberg "Vehicles" book: https://en.wikipedia.org/wiki/Braitenberg_vehicle