Trad-dance-callers

Is an American forum, dealing mostly with Squares (traditional and modern) and Contras.

English Country Dance mailing list

Is another American forum, discussing the sort of dancing that in England we would call 'Playford' i.e. dances from C17 onward, and modern dances in the same style.

For English dancers who prefer something more lively there is ECeildh, you can see archive here.
The list owner is very strict about 'only eceilidh', we get our knuckles wrapped if we mention anything else.
He says
"Better Places to post non-English Ceilidh stuff
news:rec.folk-dancing
news:uk.music.folk "
but I'm not sure about those links.

The group allceilidh is more inclusive - you can post about any kind of folk music and dance, but doesn't get many posts.

More info here