In Britain people can license the Ordnance Survey's AddressBase product, which provides a list of almost all the country's addresses, with good building location accuracy even for remote country buildings. This is obviously useful for address suggestion and geocoding applications!
Like all geodata products it's got some errors and omissions, but it's generally good (if expensive to license)
I'd like to broaden my horizon beyond just the UK. What's the best data available for France, and how good is it?