Death animations are the art of units dying. The various types have been greatly expanded in StarCraft II.
The same death animations are used for basic units in multiplayer and singleplayer, although special hero units have different death animations. Typical units have 4-5 animations, often varying depending on what type of weapon killed them (e.g. burning if killed by a hellion or colossus). The pieces of the dead unit use Havok physics, causing them to move randomly and react according to the type of terrain.
When a unit dies, its team color is set to black.
Blizzard had posted some development videos on their site.