Google Earth - NASA City Lights ∞
NASA have now made their amazing montage of city lights across the Earth at night available as a layer on Google Earth.
To switch it on, go to Layers > Featured Content > NASA > Earth City Lights, but before you do that, for maximum impact, navigate to an area you know well, like Scotland, and turn off all the other content. Then after switching to the Earth City Lights layer, try and navigate around!
It is also fun to switch on the 3D terrain, roads and placenames then fly down valleys you know, looking at how much (or little) light pollution there is.