Your list of must have addons

Here's mine:

Auctionator - Makes using the AH a breeze, better than auctioneer imo
BadBoy: Spam Blocker & Reporter - never see spam and automatically reports it to Blizz for you
Deadly Boss Mobs + all dungeon / raid sets - Must have no explanation needed
ElvUI - UI replacement
ElvUI Shadow & Light - additional improvements to ElvUI
Follower Location Info - Information on followers and how to get them
GTFO - Makes annoying sounds if you're standing in something you shouldn't be
Master Plan - Garrison missions made easier and better
Postal - Great mailbox enhancement
Rogue Spam Reborn - Not just for rogues! gets rid of the red 'that item/spell is not ready yet' or you dont have enough mana/energy/etc
WIM (WoW instant messenger) - (gives messaging it's own windows with history so you dont miss something in the chat box