As you may know, you can view Gigapan high resolution photos in Google Earth by enabling this layer (Layers > Gallery > Gigapan). But you can also view many other great Gigapan panoramas that are not published in this layer by visiting the Gigapan website.
Not all photos on this website have been geolocated and thus cannot be displayed in Google Earth. On each image page, look on the right side of the page for a link indicating that you can view the image in Google Earth 4.2 or later. Be forewarned that this site is highly addictive.
Learn more about viewing and navigating photos in Google Earth.