The 660FM packs everything except the kitchen sink. As well as a large 4.3-inch screen, it also features Bluetooth, an FM transmitter for audio through your car stereo system and the mapping, which comes with data for the whole of Europe. Expect to pay around £399.
The 200 series is more entry-level. Small/lightweight devices with an internal GPS antenna (ideal for carrying around with you) with a 3.5-inch screen, along with a calculator, clock and currency convertor on top of the mapping software.
Expect to pay around £160 for a nuvi 200.