I recently found an old map of the Heathrow area on Wikipedia. It shows the area as it was in the 1930′s, when the aiport was known as the Great West Aerodrome. You can drag the slider to fade in the current map, which I nabbed from Open Street map. Producing that was the very limit of my CSS/JS knowledge, so sadly you can’t pan around it like you can with normal online maps!
You can see the maps here.