There are several excellent videos in various formats (YouTube, blip, WMV, even the dreaded RM) available at this St. Sulpice web page. The most interesting are those of Daniel Roth improvising for visitors while calling out the stop changes: "Voix Humaine by Clicquot", "a wonderful stop, Flûte Conique, just behind the façade", and so on. Watch him stretch for the fourth manual and imagine Widor playing the Allegro from Symphonie No. 6 back back when the Récit was on V: The mind boggles!
Here is another recording of M. Roth, this time playing
in Rouen. I very much want to pick up th