Led ++

A simple typical Led ++ UI build around efficiency and minimalism.

All the important information is shown in a easy to track display. My unit frame, target unitframe and party unitframes (and raid) are all close to each other. And party debuffs which I can cure are easy to detect.

All the important buffs I get, such as Killing Machine and Rime etc. are shown right above my UF so I can never miss them. For my shaman for example it's things like Clearcasting and totems etc. This enables me to make the default buffs way smaller (see upper left screen) as I barely have to track anything in them.
Debuffs are quite huge so I just can't miss them.

A very simple threat addon which automaticly adapts to DPS'ing, healing or tanking. Just a number and small text which shows me how my threat is. I figured this works better then all the bars like Omen or sThreatmeter for example. For AoE fights my nameplates get a yellow glow when I'm getting to high on threat, and a red glow when I have aggro. Very easy to use when DPS'ing, healing and tanking.

My castbar is relative small, with just the spell I cast and the time, while my target castbar is way bigger with an icon and text so it's very easy to see what he's casting, how long it takes and if I have to interrupt it or not.

1 simple row of actionbars made to monitor important cooldowns. I 12 slot actionbar in the lower right made for spells I rarely have to cast (blessings, mount macro, weapon buffs, ...) and 1 more hidden actionbar below the minimap on my Shaman which I use for some totems (Tremor Totem etc.)

Disclaimer: The pictures are not 100% up to date, I made some small changes since but it should give you a 90% good look of what my current UI looks like.