Kings of War is a great free fantasy rules set from Mantic Games. Here’s a variant for the Viking Age
vikings
Pigs and Glory: The Viking Sagas
Pigs and Glory is a set of free wargames rules for Viking Saga Campaigns. It is designed to give some context to period battles.
Ravenfeast – Norse Saga Skirmish Rules
Ravenfeast is a set of free wargames rules for skirmishes in the Norse sagas.
Viking Battles In the Anglo Saxon Chronicles
Merlin Larson offers a list of battles with Vikings from the Anglo Saxon Chronicles. The most interesting thing he found was that – contrary to the mythology — the Vikings were not necessarily superior in battle to the Anglo Saxons.
Viking Painting Guide
Kurtis Brown offers a one-page painting guide to Vikings.
Note: the link above is dead, and an email to Kurtis bounced. So I went to the Wayback Machine and retrieved a copy of the page. It is preserved below for posterity.