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.
dark ages
Viking Flags
The Man Cave has a couple of printable Viking flags.
Free Viking Shield Decals
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.
Shieldwall Dark Ages Rules
Legio Wargames offers Shieldwall, a set of free wargames rules for Dark Ages battles in the British Isles and Northern Europe.
White Steeds and Seax
White Steeds and Seax is a variant of the Dark Age Infantry Slog rules, which include rules for cavalry.