Here’s a scan of a classic Viking raid scenario from a twenty year old Practical Wargamer issue.
Kings of War is a great free fantasy rules set from Mantic Games. Here’s a variant for the Viking Age
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 is a set of free wargames rules for skirmishes in the Norse sagas.
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.