Dawn of War 3 is set to arrive this April 27th, bringing with it a massive battle between the Space Marines, Orks, and Eldar. And if you still have no idea which faction you want to pledge allegiance to, you might want to check out the recently posted intro cutscenes.
They aren't terribly exciting or rich in storytelling, but they should at least give you an idea of why each faction is willing to throw hordes upon hordes of their finest warriors straight into the grinder. Well, except for the Orks anyway, they're here to do exactly that! Here are the videos:
On the other hand, if you would like to get a brief overview of Dawn of War 3's gameplay and overall story you can find the "Prophecy of War" trailer over here. The video features a bunch of action shots with more Orks than the eye can see, a tiny glimpse at each faction and their motivation, and some very Necron-looking buildings. Enjoy!