Earbuds with outside noise attenuation or active noise canceling will help prevent hearing loss. Even the quitest helmets allow a lot of wind noise. That plus the volume needed to listen to music enjoyably would likely lead to significant damage to hearing.
They are noise isolating, no active noise canceling though. Basically they are just part ear-plugs, part speakers.
I'm learning that active noise canceling earbuds are becoming available, but not all have the iPhone mic and controls. I'll be looking for some as soon as the prices come down.
Matt, John,
I bet if you tried it, you might change your mind. I was like-minded until I got the iPhone and tried it with earbuds. Wow, really enjoyable, especially on the longer more boring legs of moto-adventure, the riding-to-the-fun roads parts.
The first pair of ear-bud noise cancelling units I bought were Phillips brand from Wal-Mart. They worked pretty well but the little donuts fell off too easy. The next pair were Kenwoods that have a nice volume control but I don't think the work as well even though they were 3X the Phillips ones. At least the donuts stay on them.