As the name of the site suggests, it has a lot of images of more modern architecture, but it's not limited to it. If you look around on the forums, you'll find a lot of interesting (and some high resolution) images of buildings all over the world.
Might be old news to those in Chicago or around but I found this link in the Guardian today: 'When Chicago-based nanny Vivian Maier died in 2009, she left behind 100,000 negatives that no one but she had ever seen. Her work was discovered by chance by an estate agent who set about putting her pictures on a blog. Now the photographs she took on her days off are being haled as 'ranking up there' with the best in 20th-century street photography.
I know it's probably more about people but most of the scenes are outside so I thought it appropriate to put here as well.
I found this fantastic russian site a while ago. It has reference of abandoned bunkers, plants, airfields, military bases, factories, cities, hospitals, unfinished russian buildings and many more..
(you might have to use google translator to browse)