I use a car Euro Tomtom with a waterproof case and handle bar mount, connected it to an auxiliary power socket on the bike and bluetooth to my helmet. Works great for me and its interchangeable with the car. I don't find it distracting, it helps me prepair my road positioning on unknown roads aproaching roundabouts, junctions etc. :

http://www.ebay.co.uk/itm/Arkon-Bike...ht_1602wt_1118