Vranx

BTex Tiggy

Btex (for 'Bottom TEXture') is a very lightweight addon for World Of Warcraft providing Background texture at the bottom of the screen. It contains a package of unique skins, a simple to use menu for settings skins, texture height and trancparency. All skins are compatible with Xart(Ace) and ElectrofluxTextronator(Ace). I choose to do it like xArt so that any textures made for xArt or ElectrofluxTextronator can be easily used for BTEX2 as well.
Config: /bx menu
WoWInterface, Curse, Skins

ClassPortraits Ekky

This addon shows a picture of the class instead of a portrait, this works on yourself, your party and players you target.
Curse

EliteFrame Silentspy

Changes your Unitframe to either Rare Elite or Elite.
WoWInterface, Curse

kgPanels Kagaro

Create and modify panels and art. Allows you to put colored panels behind UI items.
Curse, WoWInterface, Wiki

LitePanels Katae

LitePanels is, in essence, a UI art framework. It was created to be a lightweight, "Lua-only" alternative to kgPanels. There is no in-game config. Configuration is done through editing the layout file. Don't let that scare you, complete documentation is provided in the layout file!
WoWInterface, Curse
Plugin - LiteStats - Shows stats on LitePanels

SharedMedia Elkano, Arrowmaster, Seerah

Inserts media(textures, bars, borders, etc) into LibSharedMedia's storage. They can then be selected by any addon that supports LibSharedMedia, a lot of them do.
Curse
SharedMedia-Blizzard
Dajova Shared Media
Grizzly Shared Media
Ohi's Texture pack for Shared Media
!SurfaceControl - Forces SharedMedia to return your own texture for Fetch calls.

Skinner Jncl

Changes the default Blizzard WoW skin on many UI items.
Config: /skinner menu
Curse

SquidFrame Whizque

SquidFrame allows you to change your standard WoW Player Frame. Frames include: Squid Custom Frame, Deathknight1 Greatsword Frame, Deathknight2 Longsword Frame, Rare Mob Frame, Elite Mob Frame, Elite Rare Mob Frame
Config: /squif
WoWInterface, Curse

StatusColor Slakah

Recolours the default healthbars depending on class.
WoWInterface

StatusQuo Slakah

Simple mod to change status bar textures.
Config: /sq or /statusquo
WoWInterface

Sunn Viewport Sunn

Allows you to change the size of the rendered world area (viewport) and adds textured artwork in the non-rendered areas.
Config: /sunnart or /sunn or /sa
WoWInterface, Curse, WoWI Art Packs, Curse Art Packs