While I'm sure that my earlier post was enough to convince you of their greatness, here they are, circa 1977, doing one of those amazing, I-dare-you-to-sit-still tunes, this one called "Drunken Landlady":
And this is Michael O'Domhnaill singing "Tiocfaidh an Samhradh" ("Summer is Coming"), accompanied by Kevin Burke on fiddle and Donal Lunny on guitar. From the comments on YouTube, I get the sad news that Michael has died. Enjoy his voice, which lives on.
Update: More about Michael here.