Last week, Google published a lot of new layer content for Google Earth. Read about this update on Google Earth Blog and Lat Long.
I am especially fond of the new National Geographic content for Asia, Europe and South America. For me, the National Geographic layer dovetails so perfectly with Google Earth, as NG stories are all about visual and geographical context.
If you read a story about the Inca civilization ruins in Peru, Google Earth provides you with a sense of where these structures are situated, which of course makes the Incan story all the more amazing.