The 500 has additional maps and Bluetooth. The bluetooth allows it to connect to a mobile phone, and offers some good extras. It acts as a handsfree kit - using the speaker and microphone built into the 500. Tomtom weather is a free service - it allows you to type in any destination, and check the current weather and temperature. Tomtom traffic is a subsription sevice - around 50quid a year. It constantly monitors for traffic jams, and will re route round them. There are also other services to be launched.
the 300 is 289 in PC World.