WowAce

Checks Raid Buffs/Flasks/Consumables. Tunable alerts for misdirects, taunts, cc breakage, rez, dispel and interrupt

EBB adds groups of bars to your screen showing you which (de)buffs currently affect your toon or some other units.

Unit frame addon using Ace3.

StarTip (Tooltips from Outerspace)

Numerical and graphical display of Combo Points and similar buffs/debuffs. Also tracks Holy Power and Soul Shards.

Bulk mail sending made really easy

Lightweight Chat Improvements

Display Cooldown Count of Spell Icon and Item

AutoMagicly clicks though Daily Quests, and Turns them In.

Watches your chat, flagging missplled words, and offering correctly spelled suggestions.

Configure triggers to send messages to your raid team such as timers, rotations, and health/power based triggers. Raid smarter not harder.

Keeps track of quests.

A simple combat log that displays events similar to SCT

Adds various information based on PeriodicTable to item tooltips.

Auto repair + shows durability.

A library to determine estimated range.

Violation

OneBag is a replacement for the default game bags that combines all the bags into one frame.

AddOn development framework

Automatically turns on the combat log for selected raid and mythic+ instances.