Supreme Commander 2
Supreme Commander 2 is a real-time strategy game by Gas Powered Games who also designed the first part of the series which features epic battles between hundreds of units. Compared to the second part the number of different units and buildings has been reduced, as well as changes to the tech tree and a general reduction of map size.
Even though the engine is DirectX 9, it features state of the art global illumination and handles even large numbers of objects and effects with decent speed.