Andrew Kuntz's Fiddler's Companion used to be at the Ceolas website, but they wouldn't let him update it; so it has been moved. A number of us refer people to it, as it's the best general online reference of its kind (though J C's Tunefinder is better for locating music notation), and will be still better once Andrew has sorted out a new search function.

One caveat: in order to be as comprehensive as possible, information is included from some very unreliable sources such as Grattan Flood; and because the text is quite tightly précied it isn't always possible to tell who said what and whether it can be trusted. That said, it's an extremely useful resource.