Awhile back, the Skyscraper Museum in New York City had an exhibit entitled BIG BUILDINGS. This exhibit, with an extensive online component, explored the history of really big buildings. Two categories, based on research, were created for these large structures, called Jumbos and Super Jumbos. These are buildings that are extreme, both in height and volume, relative to when they were built. Here is the Jumbo calculation methodology and here are the Jumbos and Super Jumbos built since 1950 (as of 1999, when the exhibit was held). Lots of good pictures and data for the skyscraper enthusiast.