In Dash GPS Units

In dash GPS units have much larger screens and many more features than portables do.

'In dash' GPS units features may include satelitte radio, DVD players, MP3 players, weather & traffic update services (requiring service contracts which vary greatly).

If blue tooth is important to you then make sure that it is integrated otherwise you may need to buy a separate kit.

'In dash' GPS units require professional installation and are permanently installed so that they cannot be moved from car to car. 

Having a good degree of security is important with this type as they can be quite expensive.

Confused yet? 

Regardless if you buy online or from a local retail store it would be very beneficial to visit a store where you can see and touch a few models. 

Try several out and see which ones are more 'user friendly'.  Garmins tend to be the most user friendly followed by Magelland and then Tom-Tom.