TomTom one and tom tom go are the new ones.

Tom tom one is only £205 if you shop about. These also use the new SIRF III GPS technology (you should be able to get a signal indoors!)

300, 500 and 700 are the older models. I think 300 comes with UK maps only, 500 has europe maps and 700 has bluetooth that allows you to use it has a handsfree for your mobile phone.