Here's a couple builds that may pique your interest.
Permastun Warlord's Mark build (Link)
The idea is to stack curse effect and curse gem levels until you get 100% reduced stun recovery time. The stun equation has this subtracted from 100 on the divisor. This means your stuns will last 0.3 / 0 seconds, or infinity seconds (against non-bosses).
This build would also test the theory that getting 20% or more additional chance to stun from WM would mean literally any damage has a chance to stun, since every instance of damage would breach the 20% threshold.
Would probably delve pretty good.
Everything immunity build (Link)
This build provides the following:
Physical immunity (Shroud of the Lightless + enough CDR/skill effect duration that it outlasts its cooldown)
Elemental immunity (Impurity of Fire/Ice/Lightning with 300% aura effect = 100% less damage taken as a single source, meaning damage instance is multiplied by 1-1 = 0)
Chaos Immunity (CI)
Aggro Immunity (Shroud of the Lightless + Phase Run = 100% reduced aggro radius)
It unfortunately requires 12-16 souls per Impurity per ~40 seconds to stay perpetually active, it doesn't leave much space for DPS, and it requires the stupidest hat ever requested, but it's theoretically possible.
Decay Storm Burst build (no link)
Basically, you stack skill effect duration on Storm Burst, then pop it as soon as you spawn it. The 75% of damage per 0.4 seconds remaining is applied to Decay, which begins to effectively act as a more multiplier.
I'm currently trying this build out because it's the most accessible one of the bunch, but I'll theoretically be doing 400-600k decay damage per second without Wither, and it lasts 35+ seconds. I can either choose to walk away and tap them every half-minute, or cast other stuff while it ticks away.
I could likely pump it even more with a (good) timeless jewel.
If you'd prefer building your own skill build, I'd say these skills are underused:
Lightning Tendrils
Ensnaring Arrow
Seismic Trap