The Central Pacific Railroad Photographic Museum site maintains a page with several photos from the ceremony marking the completion of the transcontinental railroad in 1869. There are also scans of a few contemporary newspaper chronicles of the event.
Thomas Edison, America's most famous inventor, with a set of incandescent bulbs:
The cover of Edward Bellamy's famous utopian novel, Looking Backward: 2000 - 1887 (1895 edition) with Bellamy pictured:
Alexander Graham Bell, inventor of the telephone, circa 1876:
Andrew Carnegie's first steel mill, the Edgar Thompson Works in Braddock, PA, was among the first American mills to use the Bessemer blast furnace.
Frederick Taylor, engineer and founder of scientific management, circa 1905:
The Chicago Historical Society has a gallery of photos taken at the site of the 1893 Columbian Exposition: