Normally, you can not call the performance of a traditional tune a cover.
Rapalje, a Neo-Celtic Band from the Netherlands (there are Neo-Celtic bands all over Europe but the Netherlands seems to be a hotbed of another Celtic Revival), is a favorite of mine. These guys are great musicians and, as people, seem to be ready to do almost anything on stage or at a festival.
I like them so much that my daughter . . . equally their fan . . . thought I was bordering on stalking them!
Anyway, this is their cover of the heavy metal gamer song, The Crown and the Ring, by Manowar. Rapalje does it as a ballad and pairs it the ubiquitous Morrison's Jig.
http://www.youtube.com/watch?v=Myeh8sgZgp8&feature=PlayList&p=9AB7EDEC3C1753C3&playnext_from=PL
An aside: last summer, when I was so broke it was pathetic, I told a musician friend (who is quite a wag) that I decided my life needed a total change. I was going to get several tattoos and become a Manowar groupie at their Magic Circle Festival. Without batting an eyelash, he said, "I'm glad you came up with that, because I was going to suggest it to you today."
It is great to have friends you can make off-beat suggestions to while talking about music.