Alright, after redoing my interface I realized there are a few mods I cannot do without that would kick ass if Aceified.
1. Gatherer - The features from this mod that are most important are basically the tracking of high end and rare resources once mined so you can check your map and go to them when you require more.
2. Spell Alert - This mod is essential for PvP so you can time your disrupts with your enemies heals. Basically the only feature needed is the display of your targets spells cast over there head.
3. Scrolling Combat Text - I have become dependent on this as I hate watching my chat log.
4. Auto-Shout-Out - Since I mainly play pet classes this mod allows me to automatically shout out when my/my pets health hits a critical level. Most healers don't naturally watch pets for heals and this alerts them to the situation.
5. Alpha Map - Alpha map is ESSENTIAL for me for battlegrounds. The little Battle Map is far to small to correctly use to guide you to the fight when you die.
6. Hunter Anti-Daze - Removes aspect of cheetah/pact when you or group member becomes dazed. This mod saves me a ton of head aches.
7. Auto-Buff - Auto-Buff allows you to set specific buffs/tracking abilities to cast when others are not active. This makes dying and ressing painless as you don't have to press 50 keys before going back to battle.
Those are just the "essentials" I use in everyday life in Azeroth that would kick ass if they were streamlined.