The Dark Age Wargaming Blog has a nice (long) article (in multiple parts) on the historical Age of Arthur. Doing an historical Arthur skirmish game has been one of my longtime goals.
The Man Cave has a couple of printable Viking flags.
An Hour of Wolves and Shattered Shields has a selection of high resolution shield designs for Vikings. Either print them out on decal paper, or on regular paper and glue them to the model.
Legio Wargames offers Shieldwall, a set of free wargames rules for Dark Ages battles in the British Isles and Northern Europe.