Only War
"...in the grim, dark future there is." -Yoda
The latest entry in Fantasy Flight Games's Warhammer 40,000 Roleplay product line, in which players take the role of Imperial Guardsmen. Currently a pre-written adventure and pack of characters has been released, and the Beta edition of the rules is being sold online for $20 as well. This includes much of the rules, but no fluff at all.
Players roll up Guardsmen from different disciplines within the Guard - heavy weapons specialists, pilots/drivers, techpriests, Commissars, and so on. Each player also gets one or possibly more background NPC helpers, referred to as Comrades. These Comrades serve as extra hands, ablative wounds or even something for the Commissar to BLAM.
The vehicle rules look promising, and seem more streamlined than Rogue Trader's.
That aside, beside the trolls who like to post about how the mehrines are unappreciated, /tg/ has always been in love the idea of an anonymous everyman fighting in the 41st millennium. You know, the one who signed up to go fight in a big galaxy, where one needs to be pretty ballsy just to step off his homeplanet and into a festering, flaming hell where one will likely get swatted into a paste by an indifferent carnifex, axed in the spine by a guffawing ork, or have your legs liquefied into drugs that a Slaaneshi cultist will hope to snort off of some wych's ass while you watch. The one armed only with his flashlight and his faith in the Emperor to fend off the grim darkness of the galaxy. Some fa/tg/uys are probably all over this one already.
/tg/ has since created the 1st Membranes, a fan regiment made using the creation rules found in the Only War beta. They are made primarily from Psyker stock, and as a result are a regiment of gibbering, schizophrenic and/or awesome troopers who, when confronted with Orks, will either scream at the things coming out of the walls or mow down hordes of greenskins with mind bullets.