Is there a flexible "cloth-like" material that can be used as "skin" for a non-conventional wing? I am in the very early stages of playing with the idea of an ornithopter derived aircraft. The intention is to be able to scale the resulting aircraft, to passenger (or useful payload) carrying capability.

Is there any material that is simultaneously light - but also strong enough to carry the weight of an aircraft (and it's payload)?
Aircraft fabric would be too heavy for a person carrying homebuilt orni-contraption.  What you are looking for is 3M Mylar/Tedlar.  It has been used as a covering material for a number of ultralights like the Lazair for many years.