Gaston Leroux's The Phantom of the Opera (full-text) online
http://www.literatureproject.com/phantom-opera/index.htm

The parent site:
http://www.literatureproject.com/
Who are they? They also offer ebooks and text-to-speech

While we're on the subject of 19th century romances, here's a site dedicated to the numerous (yes, there was more than one) books/tales of the Scarlet Pimpernel. Showing here (also full text and also free):
http://www.blakeneymanor.com/