For now there are 8 games based on Warhammer 40k and several extensions to base games. These games are:

Dawn of War

Dawn of War: Winter Assault,

Dawn of War: Dark Crusade

Fire Warrior

Chaos Gate

Space Hulk

Final Liberation

Rites of War

The most famous (and awarded as the best RTS of the year) is "Dawn of War". The story of the game isn't completely taken from the Warhammer 40k history because it describes a long-forgotten chapter of Space Marines (never mentioned in any of books about WH40k before the creation of the game) who fights bravely against space invaders. Dawn of War brang many innovations to the world of RTS games. One of the most important is that infantry units are given orders as squads rather than as individuals which makes the gameplay easier and clearer. In addition to a typical health points, infantry units also have morale. When morale drops to zero, the squad "breaks;" and it's accuracy , damage and defensive capability reduces.