General stuff:

• LotRO.com
• Barrow-downs - A non-game-related Tolkien Encyclopedia
• Place Names

Guides and references

• The Brasse.com -- Excellent Quest Guides
• LotRO @ MMODB -- Bare-bones but often useful quest summaries
• Middle Earth HQ -- Quest Guides
• Allakhazam LotRO Database
• General Leveling Guide (somewhat dated)
• Map/Leveling Guide (less dated: does not included newer zones)
• LotRO Guides -- A few Quest and Deed Guides

Maps

• Arda Online Map -- Online, interactive map
• Middle Earth HQ Map -- another online, interactive map

Wikis

• Lorebook -- Official Lot RO Wiki
• LotRO Wiki -- Unofficial Lot RO Wiki

Characters

Doyce's LotRO Characters

Captain Info

• Captain Play-guide

Guardian Info

• Guardian Basics
• Guardian Tanking Basics
• Useful Guardian Traits

Hunter Info

• Useful Hunter Traits

Traits

• Traits for all classes

Crafting

• LotRO-crafting.com -- it is what it says

Instance List

Comparing MM Os