Necessary
ArkInventory [I haven't found an inventory mod that works as well for my needs as AI over the years I've been playing]
Some sort of bar mod [I've used Dominos and Bartender over the years, as well as a few others. Just about any bar mod is better than the stock bars]
oUF [As much as it may be a pain to make/modify layouts sometimes, I've found no other unit frame mod to be as customizable as oUF. I can always make, or modify a current layout to fit my needs without too much trouble]
Preferable
VanasKOS [I've been rolling on Arthas lately, and it's nice to keep a list of people who camped me, so I can camp them back. It also sends my list to my guildies if they run the addon, so they can steamroll anybody on the list if they come across them.
]