GPS Buying Guide
Portable GPS navigation systems can guide you through unfamiliar areas, suggest an alternative route around rush hour traffic, and perform an increasing array of infotainment functions.
Here is an excellent guide by ConsumerReports.org that takes you throw the process of choosing the right GPS device for your budget and needs. It gives you detailed information on the various types of GPS, their different features and the brands to go for. Really useful for the first time buyer.
You can start by watching this video.