This is going to be a fairly lengthy read, so you have been warned. As most of you know around here, I'm big into working on my user interface for WoW. The default interface, while functional to me, lacks in the aesthetics and lacks function for specific needs of specific specs. I've been posting UIs here ever since SSC, but have been working on mine ever since I found out you could make changes to the Blizzard UI. Whle I feel like I can make solid UIs that others can modify from there, I don't claim to be on the level of others that have thousands of downloads of their UIs. I'm a musician at heart, I don't have a creative eye to be able to create a masterpiece UI. I'm not computer literate enough to make complex changes to lua coding or to design an addon myself. I just like taking what others create in terms of addons and seeing what I can piece together.
Over time I've developed a philosophy that isn't unique or mind blowing, but it is one that works. This thread is designed to give you insight into how I think when it comes to UIs as well as some suggestions for websites, addons, and anything else that comes to mind.
My design philosophy:It's very simple when you look at it, but sometimes I make it sound difficult. My thoughts with UI design is this: If it's not 100% imperative that you see it in combat, then it doesn't need to show. It sounds minimalistic and it is. While I'm not minimalistic to the point where the only thing you see on my screen are my player and target frame, I try to show as little as possible to open up screen space so that I'm more aware of what's going on around me. I personally don't use a damage meter in game. I don't use omen. I don't use any over the top art addons like KG Panels, or Btex anymore. There are some designs around Viewports and such that I've experimented with, and have liked what I did, but I eventually strayed away from them. To me, these things cause clutter and when other addons perform their functions or 3rd party sites (WMO, WoL) are better at their job, there's little to no reason for me to use them.
To me, maximizing your screen space is imperative with the way raiding and pvp in WoW are at now. Being aware of your surroundings and what's going on around you at all times can mean the difference between a wipe and a kill, a win or a loss, a death and living. I try to set myself up to be able to know pretty much everything going on around me. I find clutter distracting, and useless information to be such a hindrance. Duplicate information such as a HUD and a player/target UF showing bug the hell out of me. There are many that will say that they need that HUD and player/target frame. I say that shows the sign of a bad player who can't or doesn't want to train themselves to become more aware of themselves and their surroundings.
I firmly believe that your UI can and does effect your performance in pve and pvp. I also firmly believe in uniformity. Matching your fonts and textures of all your addons just simply makes your UI look better. How many times can you recall me saying "Unify your fonts and textures to clean your UI up?" More times than you care to count right?

As you can see from the latest screenshot I have of my druid's UI, that I follow that philosophy fairly well. For an Out of Combat shot, I don't have a recent one that shows my bar changes like this combat shot does:
During Combat:
http://img245.imageshack.us/img245/2826 ... 193010.jpgYou notice the amount of information showing is very little, yet still tells me everything I need to know. SLDT hides, but Power Auras shows. My MSBT is set to filter a lot so that it stays readable, and the only buttons you see are cooldowns and FF for a range check. To me, things like your mounts, professions, hearthstone, form bar etc..are all things that can be hidden until you mouseover them. They are never absolutely necessary to show at any given point, but they are there, easily accessible, when you need them. My main abilities are all keybound and with Faerie Fire acting as a range check for Wrath, Starfire, Moonfire and Insect Swarm, I don't need to show them. Cyclone has since been added to my bars as a range check for Faction Champions for that spell since it has a different range. My heals are all bound, as are spells like Revive, remove curse, abolish poison, etc
My Addons:Now for those that care, my UI still uses quite a few addons, but I try to stick to addons that are very lightweight. During a state of stasis in game, my UI is only using 7 or so MiB of memory, and only gets to 12 at the worst of times in a raid due to Power Auras (the addon tends to get heavy in terms of resources, but I haven't found anything better that does what it does for me). The major addons I use are as follows:
Unit Frames - oUF with the oUF_Nivaya layout (raid frames and cast bar included in this addon/layout)
Bars - Bartender 4 with Button Facade: Svelte as it's skin
Chat - Low Memory Chat
Whispers - Cellular
Minimap - Chinchilla
Information - SLDataText with SLDT_Honor plug in
Tooltip - loltip
Reputation/XP Bar - XP Bar None
Boss Mod - BigWigs
Combat Text - Mik's Scrolling Battle Text
Cooldowns - OmniCC
Other Mods:
Power Auras - Tracks Eclipse
oUF Debuff Highlight - oUF plug in to show curses, poisons, magic, diseases etc.
oUF Druid Hots - Useful hot tracker for the time when I use to spec resto, never got rid of it.
Winter Time - for LWG tracking
perror - to cut out the red text spam
cael_nameplates - modifies the blizzard nameplates...still learning this addon
AZ Castbar - I use the loot roll plug in and totem plug in for my shaman only for this addon.
Carg_bags with Nivaya layout - bag addon
Seems like a long list I know, but it's a lot less than what I use to use.
Other addon options:So all my addons that I use might not be the best for you. That's ok, and in fact, I'm glad to hear that. If everyone used the same addons as me, I'd be extremely worried. Options are a good thing as different people have different tastes. I always recommend this website for those searching for alternative addons. It was set up a while ago but is extremely good at showing you addons you might not have heard of, or giving you a new choice for a specific need. Here's the link:
http://vranx.com/ but I'll hit some of my personal favorite alternatives to my addons covering the major categories I listed above:
Unit Frames: I used to be hardcore Pitbull user, but I tested out other options and the one I would use if I ever decided to leave oUF is Shadowed Unit Frames. It's a unit frame addon that's extremely simple to set up and out of the box, looks decent.
Bars: Dominos. Covers the same bars Bartender does.
Chat: Chatter. A bit more customizable than LM Chat.
Whispers: WIM, nuff said really.
Minimap: pMinimap, Simple Minimap, and aMinimap
Tooltip: TipTac, TinyTip, TipBuddy
Reputation/XP Bar: Nothing I've come across works like XPBN does for me.
Boss Mod: Deadly Boss Mods
Combat Text: Parrot, SCT are really the only other options besides the default Blizzard text, which works fine if you incorporate it correctly.
Cooldowns: Cool Line, Forte Xorcist, Ghost Pulse3
Vranx's site can give you more, those are just personal favorites of mine. Hopefully you guys now have a better idea of what I'm looking at and what perspective I'm coming from when I critique your UIs and offer suggestions. While everything about a UI is personal as generally you are the only one playing your characters, I feel there are some things that are black and white in terms of being good or bad. Some basic ideas that everyone should follow. Perhaps I've given you an idea as to how my mind operates when it comes to this aspect of WoW.