Here's a link that hasn't been mentioned yet:

FOLK SONG AND MUSIC HALL: The intersection of folk and music hall...

It's the creation of John Baxter:

"This site features a collection of Songs sung in the Music Halls, the stories of those songs and the people who sang them, and how these songs relate to traditional music of the British Isles. I hope it will encourage people to sing the songs, so where possible I include videos and links to sheet music .

"It also has my blog about the social history of Music Hall. I hope to comment on various ways in which it relates to the social history of folksong. I am mostly bringing together information found by others – though I occasionally delve in Victorian newspapers..."