As with a lot of games, Lotro allows for plugins to change some minor (or a lot) of things about the game.
While they're not needed at all for play, there are some nice ones that might make life easier.
I'm listing the ones I'm using as those are the ones I know best.
http://www.lotrointerface.com/ is the site I get them all from.
This neat plugin adds a new way to show the active effects on you. It makes it much easier to track cooldowns and dispellable effects. Another function this has is that you can make certain effects trigger a skill, which is useful for auto-removal of certain debuffs.
Despite the name, this one has near every map in lotro available. What it does is add a whole bunch of extra information to the maps, including npc locations, boss mob locations and other things that are nice to know. There's also the option to add your own notes and a filter list to only show the things you want.
Adds 4 buttons that light up when a certain type of debuff is on you, that when clicked activate a determined skill. It also adds a health and power bar more centrally to the screen without being disturbing.
Ever wondered how some of those people play difficult songs without breaking a sweat? They use this plugin of course (or they're just that good).
This enables you to make a list of .abc files (try www.thefatlute.com for a lot of them) that can be played with the press of one button.