I have had some success with a Lego Mindstorm using the Lejos OS. This supports USB and Bluetooth control, so you can also use a cell phone. Although I have not used a camera with this, there are plenty of tutorials online which suggest it is quite simple to do so.
It comes with a selection of sensors and wheels (the kit I bought had an ultrasound rangefinder and a light sensor) so it's really easy to get something up and running if you're more interested in programming than electronics.
The stereo camera I have on my desk right now is a Novo Minoru. It is a really cheap option but seems to work okay for simple vision tasks. It is also UVC compliant so seems to be pretty easy to interface with.