I almost always ride with tunes through my Starcom1 Advance. I always use 30dB earplugs and can crank up the volume of the Starcom through the helmet speakers enough to hear the music just fine.
I started using my 20GB iPod (hard drive version). It had to be mounted on something soft, like atop a tank bag, or else it would crash. It is difficult to manipulate the music while riding with gloves on due to the touch wheel.
Next I switched to a 1GB iPod shuffle. Very convenient, small, flash drive (no skipping), works with gloves. Cannot be charged on the road so when the battery dies, you go tune-less. Also limited amount of music.
Currently I use my Garmin Streetpilot C550 GPS with 2GB SD cards installed. It allows me to see what's playing and manipulate via the GPS screen even with gloves. Unlike the touch wheel, the GPS operates via touch pressure, not finger proximity. I already owned the C550 for the cage, and it has all the desired features of a Zumo, but is not weather proof. Just yesterday I got stuck in a really gully washer over in Vermont and had to put a zip-lock baggie over the GPS.
I'll be upgrading to a Zumo 550 pretty soon.