Are we having fun yet?
How about the "entomopter"; The blade pairs tilt , or flap, intstead of rotating. Some serious research is going into this.
http://gtresearchnews.gatech.edu/res...sp-main6_b.jpg
One question concerning the stop-rotor design using counter rotating single-blade rotors: Twice per rev the blades are on the same side. Iwould think that they would need to be individually counter balanced, leading to a solution thats twice as heavy as a normal rotor.