good topic and nice post above.
From my hometown:
The Eads Bridge http://www.asce.org/history/brdg_eads.html first major railroad bridge over the Mississippi river, and first structure to use alloy steel in its structural members, built in 1874
More modern sturctures: Hoover Dam, Golden Gate Bridge, Brooklyn Bridge
And how about one that wasn't exactly a masterpiece - the Tacoma Narrows Bridge - an early suspension bridge - check out the photos and short video clip at http://www.enm.bris.ac.uk/research/nonlinear/tacoma/tac09.gi f
The bridge began exhibiting wave motion before it was completely constructed and the motion worsened. The bridge was nicknamed "Galloping Girtie." It collapsed only a few months after it was opened for use.