My Favorites 

Lake Placid Loppet (New York)

Keskinada Loppet (Ottawa, Canada)

Craftsbury Marathon (Vermont) -- has a touring division as well as racing

Touring events 

Canadian Ski Marathon 

General 

XCskiworld events center 

Marathon series:  American -- Worldloppet -- Euroloppet 

Northeast US:  New England -- New York