As awesome as the core rule book is, theres a lot more out there. More than one man can buy in one go.
So with that in mind, what are the best expansion books to start with?

Looking for the ones that offer more for the DM to add to his game. New ships, rules on systems, planets, new ship hulls, more so new weapons for ships and celestial bodies (Stars, Black holes etc on a star map during combat) and races to encounter.

Also, are there any pre-gened adventures to run other than the one in the core book?

Ta muchy! =D

Into the Stars expands the Core game quite nicely. Battlefleet Koronus adds a whole lot of hulls to play around with and expands on the enemies. There are ideas for adventures in there. Those two are must-haves.

Into the storm it's a must. That's followed closely by battlefleet koronus and stars of iniquity. I don't love hostile acquisitions, but it's not terrible.

Of the 10 or so RT books I have, the core, Into the Storm, Hostile Acquisitions, and Battlefleet Koronus are great. Lure of the Expanse is the only campaign I have, but I always like what I read in it. Edge of the Abyss has a fun adventure in it, and some cool fellow peers of the Rogue Trader class, from the guy all other pics use as an RT (Trask) to the big man on the Expanse's corner, Calligos Winterscale. If you want your players to try and deal with these other mighty merchants, or even become their foes, this book helps know who they are, what they have, and what they do. Koronus Bestiary rounds out the critters well. I'm not personally a big fan of Faith and Coin or Stars of Inequity, but they are decent, I suppose. Navis Primer has some nice stuff, too, but it could be a bit specific, so maybe you could put it off.

Into the Storm and BFK are must haves. I really like Hostile Acquisitions personally. Its a good splat book, especially the career options imo.

Into the Storm and Battlefleet Koronus are the most important ones.
I like Stars of Inequity very much, but feelings are mixed.
The Navis Primer is awesome, but can be ignored for a while.

Edge of the Abyss has some ideas for writing your own stories, as does Into the Storm.
About the only redeeming bit about Faith and Coin is that it too has some ideas for stories, which are rather more detailed than in earlier books.

As for the actual pre-gen adventures... I'm not generally a fan of pregen adventures, I usually read them only to loot them for ideas, but I actually rather enjoyed Frozen Reaches, the first of the Warpstorm trillogy. The rest sadly did not live up to it. Nor was I terribly impressed with Lure of the Expanse, though it's certainly better that the second part of the Warpstorm trillogy (Skull Fortress was the name I think).

If you visit the support page for RT ( here ), you can find a few introductionary scenarios for down load, as well as errata and the winners of an adventure contest held in 2010. I ran Fall from Grace with decent success.

• Into The Storm - You need this to round out a lot of the rules and social situations that are presented in the core rulebook, plus it gives you a little bit of everything.
  

• Battlefleet Koronus - You can run a perfectly enjoyable campaign of Rogue Trader without this, but your Void Combat sections are going to suck. This book makes Void combat fun and interesting, and without this book you're missing out on something highly enjoyable, but it's not strictly speaking necessary.
  
• Lure of the Expanse - This is theoretically a single adventure book, but this is actually a book that provides a strong section on how Footfall works, a series of adventures that work fantastically as a standalone adventure, and a great example of how to throw together a climax. You also get eight other Rogue Traders each of whom are not major players, but are all distinct from each other and can easily flavour your campaign.
  
• Koronus Bestiary - I find this book does for ground combat what BFK does for Void Combat. There's sections on individual monsters inside of the Expanse, sections for particular faction enemies, a way to generate your own monsters, and each section contains a very strong
  

• The Frozen Reaches - This is part one of the Warpstorm Trilogy, and the other two are not going to make my list because I find them a little too railroady and closed focus. The opening book is fantastic though, and Damaris can very easily become a fixture in your campaign due to the facilities it offers, as well as access to the Imperium it provides.
  
• Game Master's Kit - The screen is always fun to have, but the real strength from this is the Svard adventure, which is extremely interesting and gives a great feel for the Yu'Vath as the long-dead horrors that are still around.
  
• Hostile Acquisitions - Provides a good amount of backstory and some more factions to throw against your players. Did not actually feel as strongly criminally-themed as I had expected, but still quite good.
  

• Faith and Coin - This book single-handedly provides a huge amount of missing backstory to the Koronus Expanse and makes it feel like a more populated and storied place. This being the most recent expansion it makes this feel like a bit of a retcon. Also if you're interested in running a very Radical campaign, you won't get very much out of this.
  
• Navis Primer - Provides the most enjoyable Xenos class so far (Weirdboyz) and more Psychic powers and enemies and rules. It's very heavily focused towards Navigators and Astropaths, and Psychic characters are the best suited for Psychic enemies, so this is a very specialised expansion.
  
• The Soul Reaver - Dark Eldar are a highly contentious group, and this book gives you both rules for how to play them and an adventure revolving around them. The adventure is quite strong, although it focuses on a particular moment players may find unfair. It also has "The Dark Kin" as a free web supplement... that really should have been included in the book.
  

• Citadel of Skulls/Fallen Suns - The other two parts of the Warpstorm Trilogy. They're very much on-rails and action focused, so if your group is into that they'll probably very much enjoy them. I feel they don't add much to the narrative of the Koronus Expanse however.
  
• Edge of the Abyss - This book provides a little bit of everything, but is outclassed by everything that has come earlier. It's got some stories for the major Rogue Traders in the Expanse, and a little bit of backstory, so it is definitely worth having, but is also not "essential".
  
• Stars of Inequity - Colony generation rules are a little fiddly, but they're fun to have. I also like the treasure generator, and the backstory provided in this book is good, but there's nothing in this book that makes me think "I have to have this". Still good, but just like Edge of the Abyss I can't rate this as essential.
  

<sub>If I recall correctly, one of the developers commented that Into the Storm had all the stuff they wanted to put into the core rules but couldn't due to space constraints. That one is essential. After that, I'd recommend Battlefleet Koronus and Hostile Acquisitions as backup; both of those have some good stuff. If you're flush with cash, I'd add Koronus Bestiary and Edge of the Abyss for background information as well.

As for published adventures, there are five full length ones: Lure of the Expanse, Soul Reaver, Frozen Reaches, Citadel of Skulls, and Fallen Suns. (The last three are a trilogy.) The first two are decent, the remaining three have their moments but aren't that great. Citadel of Skulls and Fallen Suns, in particular, are railroady... The Svard adventure in the GM's screen is short but sweet. (Though be aware that the final boss is really nasty.)

Cheers,
- V.</sub>

_{(Edited for font size. Bad forum software! Most readers don't have microscopes!)}

Heya,

Into the Storm, for sure.

Very best,

For players the two books you NEED aside from the Core Rulebook are Into the Storm and Hostile Acquisitions mostly because of the armories and the alternate ranks but also because of the setting fluff on major things like starship stuff, Port Wander and exactly how much you can expect to get away with before any given branch of the Adeptis decides to murder you. Navis Primer is optional but I suggest conferring with your GM on how much you want to incorperate into the game because that book is a fifty fifty split between cool supplemental things and gross over complications of existing mechanics. Also all the alternate ranks are terrible, they come with sh*tty bonuses, restrictive fluff and godawful penalties.

GMs need the same and they also need the Bestiary and Edge of the Abyss, I adore Edge of the Abyss it's so full of content. You can build entire campaigns out of ideas you get after reading three pages of the thing. It's so full of monsters and locations and lore it's awesome. Bestiary provides a really codified way of generating feral mooks, I'd argue potentially too codified in some respects but it's a great tool for generating rural encounters.

Battlefleet Koronus like everyone else says is a must for any sort of at all Starship oriented game, although my personal advice is that if your players are all new to the game and especially if you are too just stay away from Starship combat or complex starship mechanics until everyone has learned, retained and gotten comfortable with the rest of the system. Starships are an entire different game it's sometimes too hard to learn both games at once and the truth is it's hard to mesh them well even if you have a very good grasp of both. So save serious Starship **** for later on, we've been playing for about a year now (missing many weeks) and we're just feeling comfortable with starships now as a consistant part of our game.

In myexperience, Navis Primer is really nice if and only if you have a Navigator/Astropath.

If these are covered by NPCs, don't bother.

Into the Storm I'd consider a must-have, it's pretty much (as said before) Core Rulebook 1.5

Edge of the Abyss is very interesting as well, with lots of background and boatloads of ideas for campaigns and adventures

Hostile Acquisitions is... nice, with cool additions to the armory, especially when you have players going for a more criminal style.

Battlefleet Koronus is a must-have when involving ships heavily. Finally Torpedos, Nova-Cannons, Small-Craft Operations, I love it. It also has a nice fluff-part about voidships and the navy.

Navis Primer is... useful. Interesting new ways for Warp-Travel and Astropathic Communication, but if you don't have Navigator and/or Astropath in your group, don't bother with it.

Koronus Bestiary I quite liked, with Adventure-Ideas based on the various beasts inside. Not really necessary though.

Stars of Iniquity I do not have, it seems interesting when going for that kind of play though.

Faith and Coin , I can not judge since I don't have it. Yet, probably.

As for the Adventures...

Lure of the Expanse is by far the best. Our group played it for half a year, we had A LOT of fun, and the whole adventure is geared towards being expanded even more, especially with the Bestiary or Edge of the Abyss. It also has nice Fluff for various locations in the expanse.

The Soul Reaver is... interesting, but has it's weaknesses. It does have a nice section on Dark Eldar gear and background, if you're interested in that.

Frozen Reaches is nice, needs a bit of work here and there, but still a very solid adventure.

Citadel of Skull is, in my opinion, the weakest of the Warpstorm-Trilogy. Nice Heist-Idea, but it could've been a lot better I think.

Fallen Suns is... a very nice way to show the players something great, make them feel special, but as an adventure, it needs to be expanded upon... it always struck me as kinda... short, compared to what it'll achieve.

For the Gm I recommend (In order):

1) Core Rulebook

2) Into the Storm

3) Battlefleet Koronus

4) Stars of Iniquity

5) Koronus Bestiary.

6) Navis Primer

I did not find a lot of use in Hostile aquisitions but my group has not wanted to go "pirate" thus far so maybe that's why!

The various adventure books are good if you like pre-made but I only find them useful as background material.