I'm having a hard time narrowing this down to a favourite.
I love G&S. I was lucky enough to see the D'oyly Carte company on tour back in the 1970's. It was an amazing experience.
http://www.doylycarte.org.uk/
I won tickets to some other show by going to the theatre box office and singing a couple of choruses of Poor Wandering One.
Loved Rent. Am nuts for The Producers.
I've been lucky enough to see almost every production staged by Opera Atelier since their first mini-show in the early 1980's. I consider a lot of their work light opera/musicals vs opera. Extraordinary productions.
http://www.operaatelier.com/aboutoa/prod_touring.htm
I enjoy most of the Fred Astaire/Ginger Rogers films, particularly The Gay Divorcee and Flying Down to Rio. I'm kind of goofy for the dance routine for The Continental.
Woody Allen's Radio Days.
so many more
edit: The Corpse Bride
the 1988 version of Hairspray