Retribution is a stand-alone expansion for Dawn of War II. It includes ALL the multi-player aspects from Dawn of War II and Chaos Rising, as well as an extra race. Plus, there is an new single player campaign (actually 6 new storylines).
The new game has gotten rid of Games for Windows Live, so it will not be compatible with the first two releases (but your stats will transfer).
Go here and register for a key. Exact details are on the front page.