Undead strategy guide @ StrategyWiki
Detailed guide on playing against different races and multi-player.
Undead strategy guide @ WarcraftWorldNow
Guide on playing units, building structures and leveling your heroes. Detailed and simple.
Undead strategy guide @ GameFAQs
Detailed information on units, structures and heroes. Includes strategies for good offensive and recipe build orders.
Undead strategy guide @ IGN
In-depth strategy guide. Must see.
