Daemon Hunters! I can tell I'm going to be really stretching for ideas after I've done five or six power armored armies!
OK...let's focus on Grey Knights for this army. Good anti-infantry shooting, good close combat, fearless, some anti-psyker stuff.
How about an army of Necron Pariahs? A force of some rare alternate type of Pariah, or some Tomb World that got cut off from the rest of the tomb network and is still using some outdated prototype version.
So how could this work out using the DH codex?
General: Good saves, "C'tan" type ranged weapons that ignore invulnerable saves, some anti-psyker stuff. Some stuff can teleport, which could either be actual teleporting or burrowing up like Flayed Ones and Scarabs. "Warscythes" can easily represent Nemesis weapons and storm bolters.
Pariah Master (Grey Knight Hero)
-Solid HTH monster, add in a psychic hood for more "abomination" effect and a psycannon or psycannon bolts for more invulnerable save ignoring.
Heavy Pariahs (GK Terminators)
-More warscythe choppiness, with option for psycannon or incinerator to bypass invulnerable saves.
-3+ save, choppy, good shooting on the move, some weapons that can ignore invulnerable saves.
Pariah Teleport/Tunnel Attack (GK teleport attack)
-Same as above, but Deep Strike.
Pariah Cleansers (GK Purgation Squad)
-Load up on either pyscannons or incinerators. I imagine incinerators would be more fun, big necrodermis shrapnel sprayers or somesuch.
Pylon Attack (Orbital Strike)
-Nearby Pylon is targeting the battlefield.
Tomb Crawlers (Land Raiders)
-Either tracked vehicles or large tomb spyder like things that roam the tomb world carrying Pariahs around. Could either have regular doors or short-ranged teleporters to represent squads embarking/disembarking.