If you are looking for a super-simple drawing whiteboard where you can have more than one person contributing to the visual work, these are three simple solutions I suggest you explore:
Awwapp: http://awwapp.com/draw.html
(no ads)
DrawitLive: http://demo.drawitlive.com/
(no ads) (integrated chat)
Flockdraw: http://flockdraw.com/ (ads supported)
(integrated chat)
(Suggested by Robin Good)
Via Robin Good, veroni