WowAce

A UI for searching the guild roster.

Friends & Guild Data Broker plugin.

Combine

A tool to appraise, estimate, or judge your equipment against the equipment of others.

Creates new chats with guild channel functionality

Bidder for DKP points. Usable as standalone bidder, or with DKP - Manager to manage points.

Uses guild notes to add alts' main names to chat windows and other places

EasyDKP

BossList

Loot management tool

TGuildFrame

Angry Raid Points Client

Tracking and ranking of dps/hps in a guild.

HazLoot

JasonQuest

Saves contents of your guild bank and sends/receives updates over the addon channel

Note + rep tracking for players, with guild data sharing.

Displays online guild mates.

Meeuuuh

In-game EPGP guild helper, supports standby, main/alt shared pools, minEP, offpecGP. Fixed price list with progress multiplier.