Personally I do all the options even though my Shoei XR-1000 is pretty quiet.

Short trips (up the road etc no 100km/h areas) - I just pop my helmet on.

Medium trips by myself - Sennheiser CX300 headphones with the iPod. Make sure the playlist isn't toooooooo agressive otherwise I find myself tempted to split at 150km/h on the back wheel.

Group riding - MotoSafe ear plugs - Can hear everything. They just cut out the wind. At $49 I should have just got the Plugs 4 Lugz ones (and I will) as the MotoSafe ones do fall out occasionally.