I have just been shown a great website called Where’s The Path. Enter a location or postcode in the box in the top left hand corner and the screen will display the OS map on the left and a Google Earth aerial photo view on the right. Very useful for comparing map data to what is really on the ground.
For a more detailed explanation, Tim Rylands, (who always seems to be one step ahead of the game!) has relatively recently discovered it and shared it too!