[JohnS]

Noise isolation is extremely important unless you like the idea of needing hearing aids at 40 (like my dad). Freeway speeds cause noise in excess of 100 dB inside even full-face helmets. Look up OSHA guidelines for yourself.
 
I use MEElectronics Sport-Fi M6 (which are on Amazon http://www.amazon.com/gp/product/B0038W0K2K/ref=oh_details_o05_s00_i00?ie=UTF8&psc=1) 
 
Pros:
Passive noise cancellation (I can and do take these shooting) the cancellation ensures you're not pumping your ipod to max volume and just adding to your future hearing loss
Comfortable (I've gone between Albuquerque and Tucson three times 8-ish hours, and they do just fine)
 
Cons:
The little rubber tips have to be cleaned every couple months (with daily use in excess of 3 hours) or else they start falling off
I have a pair in orange and one in black, and unlike the black ones the orange doesn't have the no-tangle cable - so get the black ones
 
Listening to music/podcasts/audiobooks helps keep me awake and alert on long-haul trips, and it's more fun tearing around a corner listening to some Dropkick. I've never been distracted by it and can still hear a car coming up on me, but if you find it distracting go with some quality hearing protection instead.

 

[Addicted2Riding]

I agree 100%.
 
I have a long commute to work everyday and would not know how I would survive without listening to music. 
My bike is very loud, around 7K rpms without earphones on, I feel like i am hearing a ringing noise after 15 minutes of riding. The damage wind does is definitely there. No doubt. So for me wearing earphones is a must. I don't think I've still found the best pair of earphones to use under a helmet. 
 
For those of you that feel the same as I do check out this site I ran into : www.motorcycleearphones.com
Apparently these guys are building earphones designed to be used under motorcycle helmets. I'm actually looking forward to see what they release.  

 

[Stepan]

I was looking for this kind of earphones to ride with also and ended up with Moxpad X6. Interchangeable cable, price under 20USD, but the most important part is their width. Its only about 1 or 1,5cm, they are rally low profile and don't stick anywhere. You can give it a shot on eBay or Aliexpress.