Omen Threat Meter

This one pretty much explains itself. Omen Threat meter tracks the threat of everyone in your raid. Everyone should have this, as it helps with tank to tank agro during fights where you must switch back and forth between multiple tanks, as well as making sure no one rocks the dps so hard they pull agro from the tank.

Quick Mark

Quick mark is a great addon for tanks, and raid leaders. It helps move things along much quicker on trash pulls and can mean the difference between life and death on bosses. No more right clicking then trying to find the correct icon. It's all easily at your fingertips.

Boss Tactics

One of my absolute favorites. Boss tactics not only provides an easily readable strategy to the boss but also gives you an image showing where everyone should be standing and how they should move. I know before fights where we bring someone new in we have to explain the entire fight over again and it can really slow raids down. I suggest this be on any raiding guilds 'Must have X Addons to raid with us' list.

Deadly Boss Mods

Deadly Boss Mods is an asbolute must have. I can't stress this more, it makes every boss fight so much easier and keeps everyone in the know. It gives timers and raid warnings for boss abilities, and is without a doubt one of the most useful raiding addons out there.

Skada Damage Meter

Some might argue that damage meters aren't a necessity, they're a bragging right. I disagree. Every raid leader should have some sort of damage/healing meter. When you're trying for a boss that you know you'll need the absolute best in the guild on you want to know who that is right? You want to know who can push out the most damage and who can heal the greatest right? Definitely a must have.

A Customizable UI

The most important thing you can have. You need to be able to know where your spells are, where your own frame is, as well as where the rest of your raids frames are. My recommendations: Don't have a bunch of clutter and junk all over your screen. Keep it simple and to the point. Don't have your frame and your targets from half way across the screen from your raid frames. You need to be able to target and cast quickly. Bind your keys, make macros, do whatever you need to do to keep your UI as clear and straight forward as possible.

On that note, I bid Good Luck to you all!

~Aenorn