There's been a lot of back and forth in the last week over the Alliance Wheel o' Dewm, and the fluff/lore in general, so how about we compile some resources for those of us less versed in the history of 40K? I'm still a fluff greenhorn, but I'll get it started. Please reply if you've got any nice sites or books!
According to 6th edition 40k the ally wheel is pretty accurate.
I myself don't agree with some of the "friends" that don't make since but oh well
The Lexicanum and the Wikia are the best sources I've found. You should have most of your questions answered there. There are many specifics within the fiction that may be difficult to find but most of that won't be relevant to the LCG.
Often the question asked is "what novel(s) should I read to become familiar with the setting?" The problem with answering this question is that every single novel and series covers a small part of the setting as a whole. No matter which book you read you will learn at best a siloed portion of it all. I've read an embarrassingly large amount of 40K & 30K fiction and I know next to nothing about the Tau, Necron, Eldar, Ork's and many others. Regardless, I'll try to answer the question. Everyone has their favorites and I can't say there's one "best" entry point. That said, if you put a gun to my head I'd say read The Founding by Dan Abnett. It provides a good entry point to the 40K universe mostly because it shows it to you from the perspective of an Imperial Guard (IG) regiment, i.e. a grunt. The IG is one of the factions in the LCG so it should at least show you what that's like. The series is fun as hell, keeping in mind that like most gaming fiction it's pulp popcorn fun.
I'm also a big fan of the Eisenhorn/Ravenor Inquisitor series but that won't have any relevance to the LCG. If you are thinking of playing Dark Heresy however, it's perfect.
If you want to learn about Space Marines (SM) you first have to understand that there are countless chapters (once upon a time called Legions). The SM that appear in the LCG are the UItramarines. In the past they've received a bad rap for being boring and one dimensional especially when compared against some of their brother legions like say the Space Wolves. Dan Abnett has made the UItramarines more interesting in a recent novel but telling a new comer to read Know No Fear would be counterproductive seeing how it's one book in a very long and ongoing series about a little something called the Horus Heresy.
I could go on and on but allow me to make one suggestion. If you are completely new to the setting and play video games, give Space Marine the video game, a try. It has Ultramarines, Imperial Guard, Orks and Chaos factions represented. That and it's one of the funnest games I've played in years (this coming from someone who doesn't play all that many video games). In about 8 hours of pulse pounding, adrenaline fueled game time, you will understand what it's like to be an Ultramarine.
Feel free to ask questions. I'm a bit of a lore fanatic but not an expert.
As someone who was really serious about getting into Warhammer 40k (right up until I actually started learning to play) I looked around for lore and Vaults of Terra is really quite good. It is made by a fan as dedicated to the lore as some GWers are dedicated to the actual game. Also Space Marine is awesome. I dunno' how much it taught me as far as 40k lore but still a great time!
For more Ultramarines fiction, I would suggest reading the novels written by Graham McNeill.
They follow the adventures of Uriel Ventris, captain of the 4th Company. In my early days of playing 40K I saw the Ultramarines as rigid and boring. These novels brought them to life for me and made them more interesting.
I can't remember the details of all of them but the Tau, Chaos, Tyranids and Astra Militarum (Imperial Guard to my generation!) are all featured at variosu stages.
Learn your lore... What bull. 40K changes so much and so often there are NO firm threads in it from codex to codex. Anyone that says... This is the history of X is just showing that they no ******* nothing about 40K.
Entire faction histories are completely re-written and it is a sign of how noob a player is as to what "layer" of fluff they pick.
40K was recently described by a guy on CGDB as akin to Myths. I completely agree. There isn't any right or wrong. The wheel in this game or the new blood angel histories, or the completely ass backwards ultramarine stuff is as valid as the old stuff.
Fluff used to be sparse, with players making it all up kinda like a RPG. That is the true 40K.
You are mostly right, booored. Back in the day the fluff was an excuse for the models to be fighting. Since then, in the 25 years or whatever has passed, the demand for concrete fluff has grown to the point where GW is trying harder to keep that stuff consistent. It has grown out of control with dozens of authors trying to fit stories within the existing fluff and still keep it all together, but it's a money maker for them. Look at newer companies (e.g., Spartan), they have very sparse fluff too but it's probably by necessity.
If you fancy yourself old school you probably don't like all these kids on your lawn with their strict attitudes towards fluff, but that's what nerds are: people who thrive on knowing minute arcane things regarding fantasy worlds. I don't find it appealing to argue over whether or not the Black Templars would help the Eldar in one specific situation, but there is no harm in people wanting to read about the Emperor or whatever.