The two most common motorcycle specific Sat-Nav systems on the market are the Garmin Zumo range and the TomTom Rider. They retail between £300 - £400 and although they might seem expensive, for your money both types offer tried and trusted navigation equipment, designed specifically for use on motorcycles (i.e waterproof and user friendly with gloves on).

You should spend as much as you can on your Sat-Nav and make sure that what you are buying is of good quality (if its neither of the above brands) and designed for use on motorcycles. However, if you shop around you should be able to find a good discount off a Garmin or TomTom.