Sites using HD View
xRez Panoramas
xRez has also been creating Gigapixel panoramas. View them on their site
using a javascript viewer or here using HD View.
hdview.at
Bernhard Vogl of Vienna, Austria has a great set of Gigapixel imagery of places in Europe on his hdview.at site.
Harlem-13-Gigapixels
A massive 13 Gigapixel panorama created by stitching 2045 12 Megapixel photographs.