Interesting post, JK. I have heard recordings of the organs at Royal Albert Hall and St. Paul's Cathedral. There are also some very good organs designed by Willis in England. Albert Schweitzer once said that the organ at St. Suplice in France was the most beautiful organ. If you ever get to the States, make a point to hear the Wanamaker organ (check out the website wanamakerorgan.com), and the organs at Girard College and the Crystal Cathedral. All the best in your studies!
As for spectacular organs the first one that comes to mind is that of the Royal Albert Hall here in London, it's just been renervated and sounds magnificent!