I used a Garmin Quest, there's a couple on ebay at the minute. They are discontinued now but are waterproof and with a RAM mount was ideal.
The only problem with it though is NO postcode search but if you get the software with it, you can plan your route on PC then send to the unit, had endless fun rides with it.

But the vibes do kill them, 2 i have been through

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or olives???
quote motonacio "this is to certify Meach is not the prat you'd think from his posts"
http://www.youtube.com/imeach