Well I thought I'd show my current UI with full explaination of what mods I use.    I tried to get as much as possible show in action.   Though a few of them are extraneous and turned off in raid settings.  

Clean Pic:

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Marked Up:

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So going down the list here's what I have.   I probably use way too much now.  lol

1.  BugSack - To catch all those mod errors

2.  Auctioneer (not shown) - Well part of my extraneous package.   Track auctions, work out average auction prices, auto undercutting by 1c, etc, etc.

3.  Auracle - This is a mod I use now to track raid debuffs/buffs.  These are set up to only appear during raids, inside instances.    What it does is allows you to set up common buffs to track.   Like for example, you want to know if Sunder Armor, Expose Armor, or Acid Spit is up, the major armor debuff.   But you don't care which, as long as one of them is up.   This mod basically allows you to group those together and light up red if they're not up.    And show you durations of the one that is up, though it's a bit weird with a constant zero for auras (lack of duration).    The icons are the last one it saw.

3a is my target debuffs, now it's a bit extraneous, I *could've* just set it up for buffs I care about.   But I went ahead and put everything in.   From left to right, Major Armor Debuff, Minor Armor Debuff, Bleed debuff, 3% crit, 4% physical damage, 10% spell damage taken, 3% spell hit, 5% spell crit, Judgement of Light, Judgement of Wisdom, attack slow, AP reduction, hit chance reduction, healing reduction, and spell cast slowing.

3b is my own raid buffs, this time it is only stuff I care about.  Top to bottom, 10% AP, flat AP, Agi/Str, Windfury, 5% crit, Kings, mark, and draenei.    Only thing missing is the 3% haste and 3% damage, but it's a bit messed up cause they're built into existing auras rather than giving a new buff.   I could put like Ret Aura in, but no way to tell of it's a ret pally's imp version.

4.  BanzaiAlert (not shown) - Big glowing screen alert with audio and text that you have aggro.   Not just the mob you're targetting.   It's if any mob starts targetting you from a distance.

5.  Bartender4 - Ma bar mod.   Basic stuff really.    5a is the main bar, 5b is my bags and shit, what's harder to see is that I set up 5c and d to be hidden until mouseover.  They're simply buttons for my mounts, professions, and other random crap.

6.  Chatter - Well switched over from prat.   Chat mod to handle various things like timestamps and shit

7.  CooldownCount - Big numbers to show CD times, flashes when they go off too.

8.  CowTip - Mouseover tooltip mod.   It's nice to sometimes have that info when wandering the world

9.  DeadlyBossMods - One of the boss mods to get.   I have my bigger short timer at 9a.  My smaller longer timers going down the side at 9b.

10.  ErrorMonster (not shown) - Suppresses error messages (or channels em somewhere else if you want).

11.  EventHorizon - The timer mod I use for the various buffs/debuffs I do.   Gives me a visual timeline on what's expiring, along with ticks for rupture and deadly.   It can also track CDs, and with a bit of fiddling, trinket ICDs.

12.  Failbot (not shown) - announces to raid who gets hit with avoidable shit.  Not dies, just hits.

13.  Fubar - A bar to plug in various info mods or options icons.   I have 2 bars, one on top for the main stuff.   One on the bottom for my FuXPFu, and the other thing is the Outfitter menu I'll get to later.

14.  Grid - For my convenience of looking at raid death status. 

15.  IceHUD - I mostly use it for a Combo Point watcher along with Energy tracker.   Health too I suppose.

16. LoggerHead - Well this is the mod that lets me automatticaly combat log raid instances.   When it works.

17.  MonkeyQuest - This is the only quest mod I use.   It's just an enhanced quest log, I drag it up and open it to list the quest I'm interested in when I use it.

18.  Omen - Whoops forgot to make it show, it goes around here when it's there.

19.  Ora2 - The raid assistance mod allowing for checks and stuff.   My main tank windows go about here.

20.  Outfitter - My item set mod.   This in particular is the bar for it if you choose to use it.   I have 1 main outfit, the rest are just various things that go in a few slots.   Like fishing arms the pole, and some fishing gear.   Mutilate arms the daggers and a couple other pieces.   etc, etc.

21.  Parrot - Scrolling combat text, let's you see all your epeen numbers.    Though it's also a good range check for melee, so you know you're hitting something.   Staring at this pic though, I decided to shrink the font.  lol

22. Pawn (not shown) - It's just a little mod for me to input my own stat weights to get a quick assessment of gear.

23.  Pitbull - The party frames at 23a, well as a party, they'd go above.   I also have a focus that's just below.  Target is at 23b.

24.  Pokedex (not shown) - Yes horrible name!   Well it's my mod to handle randomization summons of pets and mounts.   What I liked in particular was that I could set weights to each of them, so certain ones are more likely to appear than others.   Rather than an on off kind of thing.

25.  Quartz - For me, I mostly just use the target cast bar.   Nice big and blue for ease of seeing and interrupting.

26.  RatingBuster - For easy rating conversion visuals

27.  Recount - For the detailed in game combat log reports

28.  Satrina Buff Frames - For customization of my buff / debuff frames.

29.  SexyMap - Mostly for looks, and a way to move my minimap around.

30.  TrinketMenu - This thing allows me to convenient switch trinkets via pop up menus there.   Also able to auto queue trinkets that are on CD so you can use something else and auto switch back.

31.  UrbanAchiever - Just a bit of an improvement over the default achievement frame.

32.  VanasKOS - A little frame that shows me if there's horde (and alliance if you want) activity nearby.  Lists names and tries to determine level.   Able to add a KOS list where it'd flash the screen and highlight name if they're nearby.   Can even add entire guilds as a KOS mark.

33.  XLoot - Improved loot frames

Whew that was a lot to get through.    Definitely maybe use too much atm.   But dunno what I can trim.  lol       I certainly don't use it all during raids.