Forums
Veldrin's War of the Ring Forum - full of discussion about the online client and other aspects of WotR
Boardgamegeek War of the Ring Forum - another good forum, focusing more on strategy and variants
Rules Resources
Collector's Edition Rulebook (pdf)
Summary of rules changes in the Collector's Edition - for people who know the previous rules and just want a diff
Veldrin's War of the Ring Site - home to the official FAQ and other resources
Strategy Guides
Free Peoples Strategy Guide by MrWeasely
Shadow Strategy Guide by SevenSpirits
There aren't any good expansion strategy articles. Write one!
Variants
Look no further than MrWeasely's compiled list (I've also re-hosted some of the variants linked to by his post on this very site, here, since they are currently unavailable elsewhere.)