I use a Garmin C330. It has a suction cup on the bottom, I put it on the lid of the gas tank..ridden there for miles with no problem. Not fancy or pretty but it works. I, like a lot of other guys, carry a sandwich bag with me in the event of rain.
I use a 250W all the time. It's mounted on a home made mount I fabricated. I posted pictures a while back. Just look for gps mount. less than $20 in parts and a little work.
I use a Garmin Vista Hcx in a RamMount. Waterproof and uses AA batteries, no cords to run. Carry some rechargeable AA's in a ziplock to power it. In a pinch, stop at WallyWorld to buy a bulk pack of alkaline batteries, even with backlighting on a low power, about 20 hours on a set. I have a Micro SD card in it with all of North America on it.
It still can do routing, not the largest but it works for me. All I need including a colour screen.
I bought my first RAM mount from there site for retail. I then needed a xm radio mount. I bought the second mount from Amazon.com for less than half of the first. I also use the Nuvi 350. Snaps off and goes in the pocket or tourpak. Won't go on a trip without it.