Solo, Out of combat:
10 man Raid in combat:
I have gone through countless iterations of my UI and one thing that has bothered me was how off-balance the chat window always made my UI feel. I've seen many different ways of dealing with this visual balance issue, such as making a second chat window to go on the opposite side of the screen or sizing Omen and/or Recount across from the chat window to balance it.
I've never been very happy with these solutions for various reasons; I feel like a second chat window showing just the combat log is unnecessary for me as it's information I don't need to see all the time (and I belong to a very small guild and don't chat all that much anyway so splitting it into two chat windows is also a waste). UIs that are based around a rectangular space at the bottom of the screen are appealing to me, especially those that utilize some sort of background image to tie it together, because they tend to look very balanced. That said, I've been unhappy with my experiments with them because I felt like I was loosing too much screen space, particularly when trying to balance the chat window by, say, making omen and/or recount sized to match it.
What I finally came up with (after much too long a time) was the idea of balancing my UI around the chatbox. I first tried this several months ago and fell in love with the result immediately. I particularly enjoy having as much open screen space as I can, and sticking the chat window in the center let me balance my UI with much smaller elements than I had used before.
Along this same vein I have tried to cut down on clutter in several ways that are common and not so common. I've recently made the switch to having all my action bars be mouse-over since all my commonly used abilities are keybound anyway. The less common change I made was to hide my damage done in my SCT. I've tweaked my SCT many times (making it smaller, off to the side, etc) and I finally found that I was just sick of having screen space taken up by information that I never looked at in combat anyway. I've still got SCT for all the other normal combat messages, entering combat, my damage taken, debuffs gained, etc, which are the really important pieces of information to me. I've become so attached to having as little screen clutter as possible that I even turn name tags off in raids larger than 10 mans. (Thank god for NameToggleFu.)
The only other thing of note that I can think of with my UI is how I've set up dealing with my shot rotation. I've never been able to get PowerAuras to a point that I was happy with and many of the cooldown monitoring addons use bars which I particularly dislike because I am very visual and will pick up information much more quickly from an icon rather than having to read a bar. This has led me to use a combination of a BT bar and TellMeWhen with OmniCC to manage my rotation. The alpha on the BT bar is lowered a bit as well as it being click-through and hidden out of combat. TMW I use for most of my other cooldowns/abilities; Feed and Mend pet durations, CDs on FD, RF, Disengage, etc, Tracking HM and in the center by my BT bar it's tracking SrS and the Explosive Shot debuff on the target to try and help with my timing on LnL procs. I also have a large TMW icon for LnL that appears just to the right and above my character.
Main addons used:
agUnitframes
Bartender 4
Chatter
Chinchilla
Recount & Omen
FuBar with multiple plug-ins
Buffalo
Quartz
OmniCC (modified to show 1/10ths of a second)
TellMeWhen
TinyTip
and of course Ora and BigWigs