The Clocks4Bikes.com clock is awesome. I've had mine for almost 2 1/2 years now.
Cant pick just one "best accessory". It would be one of these:
The Clocks4Bikes.com clock
Fishtail Pipes
LED Turn Signal Light Strips
The Yamaha Mirrors
The Sissy Bar/Luggage Rack (gets used daily)
Spiked Choke Knob
Spiked Oil Cap
Spiked Axle Covers
Soren
