Here is a link to a great documentary on the rivalry between Glasgow Rangers and Celtic from the Vice website. http://www.vice.com/rivals/rangers-celtic-full-length
True - there was a youth game between the clubs a couple of months back that attracted a substantial crowd (and a bit of trouble)
There were a bunch a few years ago on the History Channel Under World Soccer-Height of Passion Milan Derby Boca-River Barca-Real Flamengo-Vasco Da Gama Argentine Uruguayan
I've seen a couple of games in Europe, and the best supporters I've ever seen were Celtic fans at an exhibition match at Craven Cottage against Fulham. They were going mental and singing every minute even though it was only an exhibition. Unreal....