The City of New York recently put over 800,000 historic documents and photographs on line. The site immediately crashed due to the load of visitors, but you can get a preview of the offerings from the Madrid newspaper, El Pais. A larger selection of images is available on the Atlantic In Focus page.
Most of the photographers were city employees; one of the best was Eugene de Salignac who documented the city, including the building of the great bridges, from 1904 to 1934.
I was able to access the NYC image collection on May 1st. It took a while to load the opening page, but the site then seemed perfectly responsive. A search with the term "Salignac" turns up over seven hundred of his photos.