I' have a Nuvi 550 from Garmin via the GPS Warehouse. For �300 I got the unit itself (waterproof, but no external sound option) with the car mount, a cradle with associated ram mount and a power cable.

I fed the cable along the chassis rails under the tank and up the side of the instruments, then attached the ram arm to the bar just under the screen. I don't miss the spoken directions as it's high enough to be easily seen.

I had a PDA unit on my GS, but that wasn't waterproof, and required an aquabox, but with the rubber screen in place I couldn't see the screen.

My only grumble is that it can be a pain to 'plan a route'. A to B is much simpler to set up.