The other thread is full of DK crap and has been dead for months, so let's start another.

I don't have a fancy gamepad, but my keyboard real estate is divvyed for best use. I use ESDF to move, with all of my most-used abilities around the keys (if you look closely you can see the letters on a bunch of hotkeys)
My list of mods is:
Visible:
Spartan UI - includes a package of Bartender, some unit frames, and the look and feel of the bottom of the screen
Titan Panel - top bar on the screen, with gold, bags, durability, performance, clock
Skada Damage Meters - Some nice features that other meters don't seem to have, including a built-in thread meter
Bagnon (and Banknon) - all in one bag mod
Cellular - AIM style tabbed whispers, bottom left corner
Prat - keeps my main chat frame neat
Grid - so I can see what's going on during a raid with special debuffs, deaths, aggro, etc.
Non-visible:
Auctioneer - duh
DBM - duh
Random assortment of mail mods
Clique - mostly for my druid, but i use it for casting Tricks sometimes as well
Titleswapper - Because I can't decide between Celestial Defender, Death's Demise, or Herald of the Titans, so it swaps every 30 minutes between those for me >.>
Livestock - random mount mod
PowerAuras - puts obnoxious things on my screen when i'm standing in something bad, or when I forget to put slice up.
ClassTimer - times my debuffs, etc.
I think that's it. Post your shit and maybe me or someone else will learn a better way to UI.