When I see something interesting shared on Twitter I favourite it; and then go back to look at it later.
I have a found a couple of images on Urban Change that would be useful starting points for lessons:
Shanghai 1990 & 2010 Although the image quality is not great this is still a very powerful image to illustrate the process of Urban Growth.
Original Source: http://chime.in/user/AngelaHe/chime/73286567210958848
Canary Wharf UnderConstruction
Construction of the Docklands Light Railway:
The BBC also has on their website a fantastic slideshow about mapping Africa’s largest slum, Kiberia. Some really powerful images.