If you haven't already heard of them, I rather enjoy Týr. Viking themed metal usually makes for good times.
Flames of the Free is probably my favorite song of theirs.
Speaking of Viking themed metal, Amon Amarth is rather well known but if you haven't given any/much of their stuff a listen it's probably worth your time.
Valhall Awaits Me is one of my favorites, and the album it's from is overall really good.
Fuck it, another Viking themed band. Leaves' Eyes is less hard, but still in the overall realm of metal.
Norwegian Lovesong is one of my favorites and a pretty good example of what sort of music the band makes.
I found all this music when I was in a Game of Thrones RP and was playing House Greyjoy, so I wanted fitting music for sea raider types. Viking stuff fit for very obvious reasons.