Just a heads-up (and a free bump), this time period is considered the Early Middle Ages. The Dark Ages is a largely antiquated term that misrepresents the period between the fall of the Western Roman Empire to the Carolingian Renaissance as being remarkably dull and uneventful, which is really not the case.
These pictures are taken from the Víkingr mod, which I fully recommend to the history buffs out there.
I particularly like the Valsgaarde helmet, but I would prefer being able to see the face behind the eye slots.