Google Earth and Nasa's Visible Earth are best defined on the Explore The World page on this site. They offer virtual tours of earth and space.
The rest of the links on the above tile are fantastic virtual tours of some of the best museums and Art Galleries in the world.
Visit the Louvre Art Gallery in France in unique Virtual Tours. Control where you go and what you see.
Similar virtual tours can be found at the Museum of Modern Art and the Guggenheim Museum both in New York. Saatchi Art offers you the opportunity to explore work from new artists and cover everything from Oil to Water paintings, Abstract to Landscape and even Sculpture, Drawings and Photography.
The Smithsonian isn't the only great museum in Washington DC. The National Gallery of Art is also in Washington. Check out the incredible number of collections available for viewing online.
If you ever wanted to visit the Vatican to see the Sistine chapel but can't make to Italy then this site offers 360 degree views of several high points of the museum.
Veterans from all services are represented in online museums. The ling is for the United States Air Force but the National Museum of the United States Army and US Army Airborne and Special Operations Museum The National Museum of the Marine Corps, The Naval History and Heritage Command offers several museums. If your a veteran of the Coast Guard, you can visit the Future National Coast Guard Museum and help support their efforts.
Please don't stop with this small selection. The number of museums offering online views is growing every day.