Here is an in game video featuring Tyranids
http://www.gamespot.com/pc/strategy/warhammer40kdawnofwar2/video/6196262
Here is what looks like the opening video, similar quality to the first games so kicks ass.
http://www.gamespot.com/pc/strategy/warhammer40kdawnofwar2/video/6193807/warhammer-40-000-dawn-of-war-ii-official-movie-1?hd=1&tag=;hd;3
Hrothgar's Might, Judas Bloodspire - Mordhiem
Chaos Night Lords - BFG/40k
Bretonnian, Vampire Counts - WHFB
M.Ind UNA - AT-43