Many beautiful railroad stations remain in the USA but sadly many like the beautiful large stations in Atlanta, GA and NYP have been raised. Others have been re-purposed and no longer serve the railroad. Some of the nicer stations that we have visited or have passed through.
Grand Central Station NYC, 30th street station PHL, CUS (of course) King Street Station Seattle, Union Station Denver, St Paul Union Station, Washington Union Station, Cincinnati Union Station (now mostly a museum), Indianapolis Union Station (now mainly a hotel)
Other nice stations that no longer serve passenger rail that have nice architecture: Cheyenne WY Station, Kansas City Union Station, (hotel- but tracks are still there) , Lackawanna Station, Scranton, PA (hotel but tracks are still there) Minneapolis Station (now hotel only), Ft Wayne IN Station (restored and begging for train service to return), St. Louis Union Station (hotel)
Vacant Derelict Stations: Detroit Union Station and Buffalo NYC Terminal (too sad to discuss)
The list can go on and on but we would have to say that our favorite is 30th Street Station Philadelphia. It hasn't been chopped up and redone as a hotel and the Acela Lounge is well maintained, not always crowded and offers easy direct elevator access to the platforms below. Ted, the lounge attendant there is a super guy and has been very helpful. He's made all of our visits there very pleasant. Four stars for Ted.