This extremely clean, sleek UI is incredibly easy to install. Just download it, pop a couple things in your WoW folder, log on and type /sui and it sets itself up! You don't have to spend hours trying to replicate what you see in the screenshot... it basically "just works".
More screenshots, download, and a video install tutorial can be found at Spartan User Interface.
I didn't create it, but I really love this addon set and figured somebody here might find it useful.