Passive Noise Reduction
I'm a military pilot with some significant high frequency hearing loss. I've found it a great help to use custom made ear plugs (Etymotic Research ER-15s) under a normal headset. The ear plugs will reduce the ambient noise of the aircraft, and will allow a greater signal to noise ratio, increasing the clarity of speech on the radio and intercom. I have used this combination on a variety of fixed wing aircraft, and it not only makes it easier to hear, but also makes flight much less fatiguing.
I'm not sure if a hearing aid will make a huge difference if you are in a noisy cockpit, as it would amplify both the speech that you want to hear and the aircraft noise that you are trying to filter out.