One of these (Outdoor Gear Adapt bluetooth adapter)
and a pair of these (Plugup S-plug earbuds)
are close to perfect for me.
I can't say enough good things about those earbuds. Great noise isolation, great audio (which you can play quiet because the buds isolate so well), and they don't stick out AT ALL so there's no pressure from your helmet.
If I want to I can stick the BT adapter inside my helmet chin bar (patch of velcro) and control it with with my lower lip... weird, yeah, but it works.
Usually I don't bother with that. The BT adapter clips nicely onto the neck of my jacket.
I only use BT when also using my phone for navigation and such. Phone is clamped to the upper triple. Waze is great for alerting me to the presence of Blue Clad Enforcers of the Law. Best nav app I've found for motorcycle use is CoPilot, because you can display turn-by-turn directions instead of maps.
For my commute, I just stick an iPod nano in my jacket pocket and plug the buds into it. Simple, easy, works great.