Awesome finds Skandinav. My bet is that most of them (except that 1200 thing from the orkneys and maybe Regin smiður (not the lyrics though) are from a bit later, like 1500, or maybe even 1700 (Hardingfele isn't that old)... but judging from the sound, it all works for the mod.
I have, however, been toying with the idea of finding Rolandskvadet in Old Norse. One of the Norwegian kings, I think it was Hákon V, had lots of the european knightly literature, such as Tristram and Isönd translated into Norwegian. I know Rolandskvadet was one of those, but we can't have the modern norwegian version.
Alright, it appears Le Chanson de Roland was translated as part of Karlamagnús saga og kappar hans. It's purely prose though.
Olafur Liljurós is an icelandic medieval folk song. It's from the ca 1500 though, but apparently, icelandic folk music is very representative of a style that's been lost in the other nordic countries (from wikipedia), and is probably completely representative of the period.
http://www.youtube.com/watch?v=zcb1bAM9uss
I found this though...
http://www.vocesthules.is/
probably the most serious "medieval music group" ever... I'm just gonna say: wow.....