My favourite version has been done my my favouritest musician ever, Loreena McKennitt, and it appears on her The Wind That Shakes the Barley CD. Here it is:
Loreena can do no wrong in my world!
And here is Lyriel's metal version. It's fantastic. Take a listen:
I love how fast it is, I love how edgy is is, I love how you can headbang to it. Great job, Lyriel!