I really love the Alternate Ranks system in Dark Heresy, with a special place in my heart for Rank 0 alternatives. What are all of your favorites?

The Cyber-Mastiff Handler (Tech-Priest, Book of Judgment) is my favorite, though the Verispex Adept is also pretty amazing. Something that completely changes your style of play and adds a fun level of character complexity. The Maletek Stalker is also super cool; nothing quite like a heretical tech-assassin powered by a Warp reactor.

I’m partial to the Sister Hospitaller and the Ordo Sicarius operative, but the one I like the most we’ll have to wait a few weeks before I’m allowed to talk about it.

BYE

Warden of the Divisio Immoralis (IH) has some great options

Metallican Gunslinger is a cool one as well for pistol folks

Mortiurge always sounded cool, but taking it in place of Arbitrator (or higher) seems a bit pointless

Cymbel mentioned it.  Mortiurge.

Makes me feel like Dirty Harry.

Demagogue and Malefic Scholar, applied to a cleric (works best combined with a Heretical Sect background). Doesn't makes you an outright heretic, but allows a great deal of 'creative' approach to any problem

I love the fluff of the Mechanicus Secutor, though it's advances are kinda silly.

The Mech-Assassin from the Lathe Worlds teaser looks damn nice, too. What can I say, I'm a sucker for all things related to Mechanicum.

The Cult Stalker, i think its called, from Daemon Hunters. I love the idea of infiltrators, and this guy is amazing at it.

Templar Calixis - cheap WS for battle psyker. Also Secutor, Metallican Gunslinger, Penal Legionnaire and Malefic Scholar. 

 I'm biased, but I absolutely love the Transubstantial Initiate as a Rank 1 alt. It completely changes the way the character plays, and gives them an early boost to psychic abilities. There are really no drawbacks or things you miss out on at all. It's awesome. 

I really liked the Metallican Gunslinger, but as I am doomed to be a Gamemaster for the rest of my life, I won't ever play one…

In my group I have a Mortiurge of the Divisio Immoralis (Warden instead of Regulator and Mortiurge instead of Intelligencer), a Telepath Psyker as Legate Investigator (rank 4) and Agent of Reliquary 26 (rank 6), a Techsorcist (on Magos Errant path) a pure Assassin and a Guardsman that thought about Feral Warrior and Malfian Bloodsworn and hoped for viable alternative ranks in Only War as a supplement for DH…

The Heretek from Radical's hand-book is my personal favorite, followed by the Maltek Stalker. 

I mostly have Luthor's problem, so I won't ever get a chance to play either- then again, I can always throw them VS the players :P 

The Heretek is great seeing as he has that Scarecrow vibe- an original way you can keep the Tech-priest viable in a fight without going Secutor :P 

Sister Oblatia, all the fun of a repentia but with 100% less purity seals on your tongue and 100% more hair on your head.

There's just something evocative in the thought of taking on the sins of others to repent for (especially when it goes to like, planetary size sin) and being this lone warrior outside your cult actively honored and mourned, because your path ultimately will lead to your death.

I mostly prefer the alt ranks that represent broad archetypes, like Penal Legionarre or Hive Ganger, rather than narrowly specific options. I was really hoping that Only War- back when that was supposed to be a DH supplement- was going to include a 'scout' option for Guardsmen that gave them some stealth skills at low levels, but alas…

Reaper

Sin Eater

Oh yeah, Templar Calix, Penal Legionarre and the Reaper (but is more a continuation of Moritat tbh)

Where is the Transubstantial Initiate?

Also. Verminspeaker is a neat way to do a "warg" psyker

Cymbel said:

It's in Rogue Trader: Into the Storm.