Philadelphia's and San Francisco's are both great buildings, but they seem like copies of others that we have seen. Philly's is clearly modeled after Paris' Hotel de Ville (sans the tower) and San Fran's looks almost exactly like Paris' Hotel Des Invalides, right down to the lantern on top and gilded dome. These are two great examples of architecture in the US, but at the same time they are merely pastiches.
Hotel De Ville, Paris France
Hotel Des Invalides, Paris France
What I think is a great example of architecture is Boston's new city hall. Hated by many, liked by handfuls, this fine example of modern brutalist architecture truly makes a statement, and at the time of construction pushed the avant-garde in directions not seen anywhere else. There must be other US city halls that look more modern, as I'm sure many were built in the 50's and 60's when beaurocracies swelled and needed more space.
Here's a pic, what do you think? I like to hear people's opinions on this building