A northern influence, but you should include Sweden and Denmark in there. I mean... we are the viking countries

I really hope, when people start modding, that it won't be so anime influenced like in Oblivion. I HATE anime. Its concept art is just horrible (please understand that this is just my personal opinion though, and leave it at that).
I think the worst thing that could happen is if Bethesda turned their games into Anime-style :/
Anyway the answer to this question should be obvious. A nothern influence, which is closely connected to an early medieval Europe.
You should, however, not forget that northern influence can also resemble to an indian/tribal influence. I think implementing some kind of tribe theme at some places in Skyrim would be cool. It's good with at least a little mixture.