WowAce

CandyBar style cooldown display

XRS

Visualises healing.

Automatically enables or disables combat logging based on location.

Shows you a much bigger icon selection frame

Queing of /who and SendWho() queries and a much better interface (see docs), with gurantee to be executed & callback.

Shows you the radius of your totems.

tracks and share quests between your party

ItemSync the happy item gatherer and toolkit.

Reduces interface tedium by doing the little things for you.

Teleporters in Suramar? Sure, why not?

Incubator

Babble-2.2

ArcHUD2

QuestLog

Good old LibTourist-3.0 for WoW Classic Mists of Pandaria

Displays information about the current zone on the World Map, for WoW TBC Classic

Displays the remaing cooldown of the action you tried to use

A simple slash-command-based addon for querying item information from the Blizzard servers via ItemIDs and SpellIDs.

Displays information about the current zone on the World Map for WoW Classic Era