I spend my life in a noisy open-cocpit aircraft. I've tried just about everything under the sun, and the best solution I have found so far is CEP ear plugs worn underneath a helmet / headset and hooked in to the headset.
If I'm in an enclosed cockpit then I use a Clarity Alofty (which uses the CEP ear plugs).
I've tried both the foam ear pieces and the custom moulded ones - the foam ones work much better for me.
As for the intercom - the key question is whether the noise you are getting from it is due to it faithfully reproducing engine and wind noise picked up from the microphone, or whether it is adding noise of its own. If it is the former then the first place to start is with the mic on your headset, if the latter then you need to do something with the intercom.
I've found that a Flycom helmet attached to the internal intercom of the Filser/Funkwerk ATR500 works pretty well.
Last edited by this is my username; 28th Feb 2013 at 06:23.