I believe most helicopters that use 'rigid rotor' systems (e.g. BO-105, Lynx, Lockheed YAH-56 Cheyenne, etc) are capable of these types of maneuvers (loop, roll, Immelmann) and can sustain small amounts (less than 1) negative 'g' for brief periods of time.
However, I don't know of a helicopter that can sustain inverted flight, as even for the rigid rotor systems the negative 'g's would be too great. Correct me if I'm wrong....
