The following add-ons are mandatory for being a member (some add-ons are only mandatory for certain classes or roles).

Use WowMatrix to download add-ons, more info at the end.

The list has the following layout:
Name
Target group
Purpose
Description
Alternative

oRA2
Everyone
Report raid status
One of many add-ons that show the status of the raid. oRA2 is the one that we think you shall use, but if you prefer another, such as Grid, you can use that too. As long as you have an add-on that shows the status of the raid.

Deadly Boss Mods
Everyone
Give warnings before dangerous boss attacks
Another must have add-on. For example, there is one boss that cast a spell where everyone must stand still, this add-on warns for that so that we know when it’s time to stand still.
An alternative is BigWigs which I have used before.

Omen Threat Meter
Everyone
Measure your threat/agro
This add-on helps you to not steal agro from the tank. The tanks agro is shown in red and shall always be at the top, if you get close with your threat you need to slow down so that you do not steal agro.
There is a built in agro meter now, but that one is not enough. Omen uses data from the built in agro meter.

Group Calender
This one is no longer mandatory since all our raids are now posted on the website
A calendar with events inside WoW
With this tool we can create raid events inside Wow and if you are interested to join you subscribe to the event. It is possible to set different limits on the event and lots of other things.
You can only join a raid by signing up using this add-on.

Decursive
All that can decurse
All classes that can decurse need to have this add-on. It allows you to very easy decurse anyone that has a debuff. (This is very important during boss fights.)

Focusframe
Good for classes that can do cc (crowd control)
Let you see what target you have focus on
This add-on is very useful for cc. I use it with my mage (Ewyn) to place focus on the target that I need to sheep. Then I can see when the time for the sheep runs out and easy do a resheep.
Blizzard have added some focus-control, use it instead if you want. I use that and this add-on, I still want to see the target that I have focus on.

ZOMGBuffs
All classes that can cast buffs.
Good add-on for managing buffs, perfect for Paladins.
With this add-on you only have one button for casting all buffs, and the add-on will tell you when someone needs a new buff.
Alternatives are mainly PallyPower for Paladins.

Before the raids it is important to update all add-ons, this is a bit of a hassle, visiting curse and downloading and so on. Therefore I recommend WowMatrix. With this small and simple program you can update all you add-ons with just one click. Run it at least once every day and you will never have any problem with outdated add-ons again.

/Loreno

Edit: Reposted by me during restructuring of the forum