Headset, Bluetooth receiver, GPS logger, radar detector. I have or had all of it in use. Here is a brief overview of the equipment:
While in America I learned to ride with headsets listening to music and navigation directions. In combination with the Zumo 660 I receive both wirelessly via Bluetooth. The head phone is an Etymotics ER 6i in ear head phone. It provides some noise cancellation and provides a reasonable sound.
My first Bluetooth receiver was a pair of Jabra BT3030. They are small, lightweight and somewhat rugged. But the battery does last for less than 8 hours. So I needed two of them for my full day tours and I changed them usually over lunch. Now I am using a Sony Ericsson MW600 receiver. It's battery lasts for about 10 hours.
Sony Ericsson MW600
For recording my tours I use a GPS logger Wintec WBT-202. It loggs a trackpoint every second and writes it to an SD card. A 1 GB SD card is more than sufficient for some weeks of riding. The device is attached via velcro to a little mount within the cockpit area of my motorbike.
During my time in the US I used a Radar detector. This is a very useful device which is unfortunately illegal in Germany.