I vote for the Quest as well. I've got a Quest 2 (includes full postcode search facility), and have it hard-wired into my monster, and through an autocom system, using a kit from GPS Warehouse and a RAM mount. You don't need to have it hard-wired, and can just use the motorcycle kit and plug a headset into it. Works great in the car too. I also have a RAM mount on my Honda CRF for off-roading, using it without a headset.
Completely waterproof, 20 hours battery life, and off-road tracking too (of you're into that kind of thing). Also fits in your pocket, as it's not much bigger than a large mobile phone. I reckon it's the most versatile unit available, as you can use it like a Garmin eTrex for walking or mountain biking as well.
Good bundle deals available from GPS Warehouse.
Saz