I am testing the mikrokopter platform right now.
It is much more expensive then ardupilot, but has a lot of features.
- perfectly stable and level flight, even in strong winds
- holds altitude within a few inches using a barometric sensor
- GPS navigation (position hold, waypoints, return home)
- attitude compensation for attached camera (camera is level all the time)
- can carry more than 2 lbs using 6 motors, and about 0.5 lbs using 4 motors
here is a demo video made by one of the project founders: http://vimeo.com/6194911