Official news and patch notes.
Prime Plugin - has timers for skills, call-outs for boss debuffs, puddles, knockbacks, etc.
Combat Analysis - DPS/HPS log
Debuff Vitals - Debuff tracker
Forum guide detailing how to effectively farm for Anfalas SOE for your LI.
Guide to gearing and dailies U27.2
General overview of things once you hit 130 (updated for Three Peaks!)
Newer site with comprehensive class guides based on role.
Class and raid guides (check dates).
Guides and commentary on LOTRO Festivals and more.
Most referenced resource for game info.
Solid source for plugins and UI skins.