Great collection of photos from the European Space Agency (ESA), from their Earth from Space: Image of the Week series. This one is a mosaic of Greece, the Balkans and the Aegean Sea.
Surely this could be made into a bell ringer/warmup. Check out the images for other geographic forms, and great photos of them. Nose around the ESA site, there are some great finds. Can you quickly identify this image, for example (without looking at the name of the photo file)?