Google just announced Google Connected Classrooms, which allows classes to take virtual field trips using Google+ Hangouts.
Field Trip locations include the Seattle Aquarium, Minnesota Zoo, American Museum of Natural History, the Philadelphia Museum of Art and more. More trips are coming also.
The field trips are live hosted events, but past events are archived and can be viewed later. Teachers can also work together on plans and activities.
This is a great resource for teachers and students to be able to learn and explore without ever leaving the classroom.