There is a new service in the UK called NetHousePrices that offers a free public service that provides access to UK house prices in England, Scotland and Wales, as recorded by the Land Registry (since April 2000) and the Registers of Scotland (since May 2000). I am not aware of any service like this in the U.S. or Canada, but I think it would be a useful too
You can go to Sold Prices, enter a postal code and then refine your search from there. If you need a postal code you can use SW5 0BE . I don’t know exactly where it is, but it will give you results.