I have been wracking my brain, trying to figure out what "anomaly" will plague my homebrew sector for dark heresy. I do like the tyrant star of the calixis sector, but I want something new, and fresh for my sector. Right now I am having writers block, so i am asking for any and all ideas from my fellow GMs on what the anomaly does. thanks.

Not new in concept, but perhaps helpful

The Harbinger of Nightmares:
An utterly corrupted Spacehulk which has re-surfaced from the warp and re-merged into it many times. Where it appears in a populated system, Astropaths turn mad or catatonic, people suffer from nightmares, small phenomenae and "ghostings" occure and cult activity is rising. It is fear, terror and paranoia. Attempts to enter or destroy the hulk have so far been unsuccessful as the hulk is host to a multitude of warp-spirits.... and some acient maligne entity.

The Nadir Flux

A phenomena barely explored but widly rumoured between the Navis Nobility, voidfarers and commander of the imperial void navy alike is the Nadir Flux.
This seems to be some two-point-swirl in the warp, both ends are wandering through it and one of it connects to the real world like the a swirl.

Ships encountering one end in the warp are torn of course and through warp, to be relocate into realspace after some weeks of warp turbulences. If the gellar fields do not collapse.

To this effect, ships from far far away (and much strange things then ships!) have resurfaced in places both distant in time and space.

(i.e: good excuse to throw ...something...into a system. )

This discussion www.fantasyflightgames.com/edge_foros_discusion.asp can be helpful: there some posters talk about a Dark Eldar weapon that traps and then releases black holes.
Just have a Dark Eldar spaceship transporting a bunch of these weapons explode in the sector, causing a gigantic black hole which is attracting and «eating» everything in the system.

This idea is probably better for somthing smaller like a sub sector or a system of planets, but here go:

Void terror

Through out the sector Ships of varying sizes and classes have mysteriously disappeared only to reapear as empty hulks later in, sometimes, completely different areas than where they first lost contact.

It is unknown why these ships disappeared, but all have returned with enourmous cuts and puncture wholes in their hulls, the crew possible sucked out by the sudden change in pressure, no one have survived an only the Hulks are left to tell a terrifying tale.

Howl of the Void

For almost as long as the Sector have been operational the Administratum have for short periods of time lost contact with almost entire planets. In the following years this has only grown worse until it climaxed with the Kartouran (insert another planet if you like) incident.

Kartouran was a Hive world that stopped responding, when finally the Imperial guard arrived they found a hive in complete anarchy with several thousand dead. The mutants had taken control of the world due to Las weaponry on the planet suddenly not functioning properly and the Imperial guard had to fight their way back into control.

Later Mechanicus investigations discovered that somehow most if not all eletrical technology had been blocked by something. The only evidence was a strange frequency noise found in most machines.

Later incidents have happened like the one on Kartouran, and the Mechanicus have determed that the frequency must have come from space and have named the phenomenon the Howl of the Void due to its origin and sound that is not unlike that of a howling noise left in machines after the attacks.

Here's a little idea

Eater of Minds

There's a world shunned that everyone stays clear up. The reason is that any psycher who sets fot upon the planet is within a day reduced to a vegetable state of mind and without any psychic capability. No one knows for sure why this is so, but records tells of strange Xenos ruins that has resurfaced in the past from and left entire systems around the world afflicted with the phenomena.

The Apostate Configuration

Across the sector, profane sites and vile rituals take place on countless worlds, and specific times and in specific places. These blasphemies are horrors on their own, but worse in conjunction, for the specific alignment of the times and locations of each and every defiled temple and forbidden congregation are a ritual of their own, building across thousands of years and hundreds of light years to unleash the horrors of the Immaterium. Whether guided by some ageless malice, or simply the result of dark inspiration, events both grand and insignificant have been directed to manifest this nascent apocalypse... and its culmination is drawing near.

The Transfiguration of Titus Andrayus

On worlds all across the ________ sector, Imperial citizens have reported miracles connected with the appearance of Titus Andrayus, a famous clergyman who has been dead for over a thousand years. But upon closer inspection, some of these "divine events" have dark connotations. Has a new Saint arisen, or is something far more sinister at work?

The Black Monoliths

Discovered by Inquisitorial xenoarchiologist Walder Hulter, the black monoliths of Qentus IV appear to come from a time long before the coming mankind. Made of a material that defies analysis, the monoliths are obviously a product of intelligence, but their function remains a mystery. As more of the monoliths are uncovered on planets throughout the __________ sector, the inquisition discovers that they are not the only ones aware of their existence.

thanks for all the ideas, they are really helping me get out of this writers block!

I think one of my favorite places in the games is the Processional of the Damned. Way to many fun random things you can do with that and similar warp phenomenon. I had my Rogue Trader game make a foray into the Processional to recover an ancient Eldar Ship, which brings me to my 2nd favorite thing, the Xenos Ghost Ship. In an area of warp instability you can really mess with your players, in the good way of course. I was having them roll will power checks all the time, sometimes just to confuse them, as an unstable region would do. Sometimes I would have them see things that weren't there, see each other as orks or demon, had minor demons pop up only a couple though, just enough to make them not want to take chances with what they were seeing. Oh it was grand, and they loved the uncertainty of what they were doing. Eventually they did well enough with the Missionary prayers and the Explorators modifications to the Geller field that they stopped seeing things but it was fun.

And the Ghost ship... I made an Iyanden Wraith Ship, the only things still alive on it were Wraith Guard, all the real crew were dead. But this sets up the best part for Rogue Trader, they wanted to salvage the ship to sell it to a shady group that was blackmailing them, the wraith guard and ship itself were insane from being around for so long and being constantly influenced by the warp. :-D

So much fun... I need to have that thing come back up...