My approach to my User Interface in World of Warcraft is have a unified and consistent design as to where I place everything. This allows me to swap between my various alts without too much difficulty.
Having played a hunter from Vanilla through Wrath I like lots and lots of buttons. It also gives me space for additional macros. You can say I am addicted to buttons and macros. I actually can barely play without a bar mod.
My next design principle is to smaller addons wherever possible. Each addon was picked for a specific purpose to address specific needs.
The layout for the unit frames is fairly classic, I leave a large open space below my character to keep an eye on the floor to head off its next attempt at my life.
Addon Control panel
I have spoken at length concerning Addon Control panel, set a profile for auctions and one for dungeons/raids/PVP. Turn off your auction suites when you do not need them.
I run this to keep track of alts, inventory and to provide an always on data source for my auction suite.
Makes tradechat more bearable.
Lightweight cast bar addon that includes latency.
Adds coordinates to your map, useful for when you are trying to find a quest item or vendor.
deadly boss mods
Technically you can raid without a boss mod, but why would you?
My button bar addon of choice. Easy to config and clean looking.
This puts a grid across your screen so you can line up each of your addons just perfectly. Great for the OCD among us.
Plays sound clips when you gain charges on a character. I use it to track Maelstrom weapon charges on my shaman. Much better than watching the bar fill up.
Keep track of who has threat. In my opinion it is as important for DPS to have this as tanks.
Ovale Spell Priority
Since i play a lot of alts, I cannot always remmember the various rotations/priority systems for my characters. Ovale Spell Priority helps remind me. Think of this as training wheels.
Shadowed unit frames
My current favorite Unit frame addon. I love the clean minimal look.
Lightweight square map addon. Sexy map does a lot more, and takes more memory to run.
Sunn Art Panel
Pushes the gamespace into a “viewport” so my buttons are not covering up the ever dangerous floor.
The default name plates are too big and distracting. My OCD will not let me play wit them on, but with this set to 50% I can. So much better.
Another lightweight choice for a DPS meter. Tracks DPS, Heals, etc just like recount. Takes much less resources unlike recount.
Does one thing, puts the typing line at the top of the chat window.
Other addons included for completeness: