Currently used addons.

Ever since I realized that the game's default User Interface (UI) could be altered through addons, I was hooked. I refuse to play on the default UI; it is too clunky for my liking. My quest for finding addons is ongoing, so the following list may become dated, with addons being replaced or removed completely. This is a very long list, but many of these addons are small in size. Right now, I am running at 23mb in addon memory, with Blizzard's client taking up roughly half of that.

Align: This addon places a (sizable) grid on your screen so you can align your UI components.

AzCastBar: My alternative to Quartz. ACB provides various bars so you can keep track of cast times including a flight bar.

Baud Auction: Provides improvements to the Auction House frame. Makes the frame movable, view "price per", et cetera.

Baud Bag: Customizable bag combining options, rarity colorization and more.

Baud Error Frame: Keeps addon, XML and taint errors from popping up in the middle of your screen. Errors go to a movable minimap button; great for reporting addon errors to authors.

Bongos2: One of many, many action bar addons. Will allow you to customize, hide or show action bars and certain UI elements. I will eventually switch to Bongos3.

Bookworm: Will automatically record pages from books and other readable objects you may view in the game. You can then view saved information whenever you'd like.

Butsu: Simple replacement loot frame. It is less bulky than the default loot frame. Movable by holding alt+dragging the frame.

Cala copypasta: A simple addon that gives you a copy and paste option when using color pickers in addons.

Cellular: Displays whispers in an IM-style window, including tabbed conversations. Simpler than WIM.

CloseUp: Allows you to zoom and rotate character models in such frames as the tabard designer and auction house dressing room.

Contemplate: Toggles enemy nameplate based on combat status. I got tired of hitting "v" and stumbled upon this gem.

CyCircled: Will allow you to skin buttons. This works with several addons, including Bongos2. Additional skins can be downloaded separately.

eePanels2: Allows you to import images or create frames. I've used this to create panels behind various UI elements; these panels act as backgrounds and borders. kgPanels is the successor to this addon.

Examiner: Lets you inspect users and cache the results. Also allows you to view/zoom/rotate models that you are inspecting, such as monsters, players and NPCs. I have Examiner keybound to "I" for easy usage.

Fane: Changes the appearance of the chat tabs. This is only customizable through .lua altering.

Fizzwidget AdSpace: Good ol' Fizzwidget! Always looking out for us. AdSpace will tell you if a pattern/recipe/etc can be purchased from a vendor. Great for avoiding overpriced patterns in the auction house.

Fizzwidget Hunter's Helper: With 2.4, Hunter's Helper provides the user with a window that lists pet abilities and the animals required to tame them. This also replaces the default pet training window. Very handy, in my opinion.

FlagRSP2: My roleplaying addon of choice. I won't compare this to MRP in this post, because I think the topic deserves its own. This can also be found on Curse.com if WoWAce isn't loading.

FluidFrames: Allows you to move or size frames ingame. I use this to make my minimap frame a bit larger, instead of setting the entire UI to a larger scale.

GatherMate: Similar to Cartographer, this addon will collect node locations for treasure, ore, herbs, fish and gas clouds. You can also import node locations by installing and importing GatherMateData. This addon works with Mapster.

Hat Trick: Allows you to check/uncheck (in the character frame!) whether or not you want to hide or show your cape and helm. Blizzard should have gone this route.

IgnoreDuel: Er... automatically ignores duels. You can still initiate a duel without problem. No more "lawl, im lvl 6 but i wnat to duel u cuz ur liek 20 lvls higher!"

LightHeaded: Tired of alt-tabbing to view quest details in WoWhead? Get LightHeaded!

Lithe Tooltip Doctor: Lets you reposition the tooltip. Does not customize the tooltip.

Lore: Allows you to speak in predefined languages. A roleplaying gem. One can also make their own languages and apply speech impediments (such as s-stuttering or hissssing.)

LynStats: Displays fps, time, latency, mail, experience and addon memory usage in a simple line of text. Can be edited through .lua. Very easy to remove elements (like mail indicator.)

Mapster: Similar to Cartographer. Allows for world map customization, removes the fog of war (blacked out zones) and works with GatherMate.

NameViolation: Great addon if you want to take an active role in maintaining your roleplay server's environment, or just for reporting names that are offensive. This creates an appropriate ticket for you to send to a GM very easily, and allows you to store multiple names. Play WoW, add names to the list, and before you log, send in a ticket.

NefRadar: Changes the minimap blips to nice little squares.

NeonChat: Colorized the chat frame and/or chatbox depending on what channel you will be speaking in. Also works for custom channel colors. Helps to avoid /yelling /say for example.

nSpam: No longer will I be frustrated by those "you can't do that yet" type messages on my screen in mean red.

oGlow: Adds rarity coloring to item icons.

Omen: A must for raiders, useful for those who actually care about not pulling threat from the tank and ending up as a smear on the ground. Omen... It's a threat meter.

OmniCC: Adds cooldown counter text over items and spells.

OptionHouse: Lists all addons, lets you view their efficiency, and disable/enable via load on demand ability or reloading the UI.

pBuff: Skins Blizzard's buff buttons and allows you to move them. Also adds time remaining. Seems the link is down.

PetEmote: Lets your pet speak! (Well, kind of.) Read my "Su's Su" post for more information.

PhanxChat: Various tweaks for your chatting experience; shorten channel names, change font size, etc. A new version is in beta testing.

PitBull: Heavily customizable unitframes. Unitframes being those frames that display your health, the target's health, etc...

Postal: Gives you more control over your inbox. Can automatically fill in guild members' names for example.

QButtons: Hate having to look through your bag to find that quest item you've got to use before 10 mobs smack the daylight out of you? QButtons will automatically pop that item onto your screen, where you can reposition it and use it quickly. Great for saving action bar slots, as the icon won't stick around when the item is used or turned in.

QuestIon: Quest tracker that's customizable and movable. Also adds information on the tooltip so when you hover of X mob, you can easily see how many more of them you must smite before you're done.

Rawr!: Did you know that all of the "old-world" (pre-TBC) races have an audio clip for the /roar emote? Of course you didn't - Blizzard got lazy and didn't code the audio clips to fire whenever you did the emote! Well, download Rawr! and /roar to your heart's content! Seems Blizzard got cheap/lazy/forgetful and didn't ask the Sin'dorei and Draenei voice actors to roar, so this addon won't work if you're trying to use it as a Sin'dorei (BE) or Draenei. :(

RecipeBook: Keeps track of what alts know what recipes, and what recipes you have stored in banks or bags.

SimpleGold: Displays your gold in a bar with changeable background color. Mousing over this will display total gold for all characters, with gold breakdown.

tekJunkSeller: Automatically sells gray items when you visit a vendor.

TekKompare: Lets you easily compare 2 items' tooltips (equipped and whatever you're mousing over).

TeksLoot: Replaces the bulky loot roll frame with something sleek and movable. Very simple.

TomTom: Works alongside LightHeaded to let you map coordinates and have them appear as blips on your map. Also provides an arrow, for GPS-like navigation.

Toons: Log into all of your alts after installing this addon, and it will now be able to display all sorts of information, including how much gold they have, what their professions are, what guild they're in, etc.

Tracksw: Works alongside GatherMate to automatically switch your tracking depending on how close you are to a node. Toggle tracking herbs and minerals with ease. Customizable, of course.

TradeTabs: Finally have tabbed browsing between cooking, first aid, and all of your other professions.

Valuation: Displays an item's monetary worth in the tooltip.