From Wikipedia: http://en.wikipedia.org/wiki/Anunnaki
The Anunnaki (also transcribed as: Anunna, Anunnaku, Ananaki and other variations) are a group of Sumerian, Akkadian, Assyrian and Babylonian deities. The name is variously written “da-nuna”, “da-nuna-ke4-ne”, or “da-nun-na”, meaning something to the effect of “those of royal blood” or ‘princely offspring’. Their relation to the group of gods known as the Igigi is unclear — at times the names are used synonymously but in the Atra-Hasis flood myth they have to work for the Anunnaki, rebelling after 40 days and replaced by the creation of humans.
Jeremy Black and Anthony Green offer a slightly different perspective on the Igigi and the Anunnaki, writing that “lgigu or Igigi is a term introduced in the Old Babylonian Period as a name for the (ten) “great gods”. While it sometimes kept that sense in later periods, from Middle Babylonian times on it is generally used to refer to the gods of heaven collectively, just as the term Anunnakku (Anuna) was later used to refer to the gods of the underworld. In the Epic of Creation, it is said that there are 300 lgigu of heaven.”
The Anunnaki appear in the Babylonian creation myth, Enuma Elish. In the late version magnifying Marduk, after the creation of mankind, Marduk divides the Anunnaki and assigns them to their proper stations, three hundred in heaven, three hundred on the earth. In gratitude, the Anunnaki, the “Great Gods”, built Esagila, the splendid: “They raised high the head of Esagila equaling Apsu. Having built a stage-tower as high as Apsu, they set up in it an abode for Marduk, Enlil, Ea.” Then they built their own shrines.
According to later Babylonian myth, the Anunnaki were the children of Anu and Ki, brother and sister gods, themselves the children of Anshar and Kishar (Skypivot and Earthpivot, the Celestial poles), who in turn were the children of Lahamu and Lahmu (“the muddy ones”), names given to the gatekeepers of the Abzu temple at Eridu, the site at which the creation was thought to have occurred. Finally, Lahamu and Lahmu were the children of Tiamat (Goddess of the Ocean) and Abzu (God of Fresh Water).