There is a wonderful website dedicated to Dark Heresy with downloadable adventures, GM tools, rules, etc. for the game by the community. I downloaded a 73 pg set of rules for playing SPACE MARINES!! It is professional quality and has the full career paths and everything. I am amazed. I plan on running a Space Marine campaign with it now instead of the default Inquisitor-Acolyte campaign inherent in the core rulebook.
I feel the need to reiterate that these critical charts are the greatest charts in the history of awesome charts.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.