Essential WoW addons
These addons are essential for raiding and almost all of raiding guilds require them!
Must have addons
You should use, have them on and keep them updated at all times.
Deadly Boss Mods - This is the most widely used Boss mods addon. It basically holds your hand when it comes to buff tracking and alerts you on various boss mechanics
Big Wings Boss Bods - An alternative to DBM.
GTFO - This addon alerts you via sound warning when you're basically standing in bad stuff. Just don't be that guy that stands in the fire.
WeakAuras2 - Used for creating custom alerts, custom buff tracking or whatever else BWBM or DBM doesn't track. Commonly used among Mythic raiders.