I would consider the TomTom One.
The blurb does indicate that some windscreens can interfere with the signal but the 'One' uses the latest Sirf technology and you would be surprised where I have collected a satisfactory signal :
In my brick garage, in the car, with all doors shut.
In my lounge, well away from the window.
It just seems to collect the signal almost anywhere.
The above is also not a case of the unit having already been powered up and therefore retaining the last signal but being switched on from cold with no info.
Superb bit of kit, apart from the lead that connects the unit to the ciggy lighter, that could do with being one of the curly wurly jobs.