This “The Best…” list is natural companion to some previous ones, including:
Here are my choices for The Best Sites For Learning About Famous Buildings (and are accessible to English Language Learners):
America’s Favorite Architecture features the 150 “best” buildings in the United States. It’s sponsored by the American Institute of Architects. It shows a photo and basic information on each of the top 150, as chosen through a survey. You can click on each image to get more info. This additional data is probably only accessible to Advanced English Language Learners, but the image and the description you see initially is certainly accessible by anyone. You can also vote on which you think are the best five, and then compare your opinions with others who have viewed the site.
You can see a slideshow of The Most Famous Buildings.
Famous Buildings and Structures comes from Infoplease.
Flickr has a slideshow of The Most Famous Buildings Around The World.
Additional suggestions are welcome.