WowAce

Keeps track of resurrection spells cast in a group

Piece of mind by being one with your class.

rSelfCast

Keeps track of time played and rested XP across your characters.

World of Warcraft Classic addon to display current zone information.

Helps you decide which ability to use next according to priority you set

Prompts for canceling of pet battles if no rare pet is found in the opposing team.

Auto sizes frame layout depending on group/raid size or predefined zone data

FuBar_DuraTek

Toggles player names.

Quest helping: fetching items to use, that sort of thing.

Set the clicking action for Grid buttons

LibDogTag-2.0

Complain about crowd control breaks.

Draws some lovely 3D portraits in the standard Blizzard artwork.

Shows your standings with the factions.

FelwoodFarmer

mHud_Threat

Used to visualize and change values of variables/variable-trees in game

EUF is an enhance of wow original unit frames, provides hp with both value and %, and optional 3D portrait. Simple and Useful.