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):
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.
The 19 most breathtaking buildings in the world, according to architects is from Business Insider (thanks to Michelle Henry for the tip).
Additional suggestions are welcome.