Grant s Tomb.Brooklyn Borough Hall.The Brooklyn Museum.The New York Public Library Research Library (the one at 42nd St. and 5th Ave.)The original building for the Morgan Library (they added a new, modernist section to the library, but the original building is the style you are looking for.)
Beaux arts is n architecture style derived from the Romans and Greeks. (Pronounce that Bozart) The most famous example is Grand Central Terminal. (Not Station!) Other examples are on the link below. Look to churches and courthouses that resemble ancient Roman temples.