Wikipedia describes the Anunnaki as follows:
The Anunnaki (also written as Anunaki, Annunaki, Anunna, Ananaki, and other variations) are a group of deities who appear in the mythological traditions of the ancient Akkadians, Assyrians, and Babylonians and Sumerians. Descriptions of the Anunnaki, how many there were, and what role they filled in ancient cultures and even within the pantheon are inconsistent and often contradictory. In the earliest Sumerian writings concerning the Anunnaki, which come from the Post-Akkadian period, these beings are the most powerful deities within the pantheon. They are presented as descendants of An, the god of the heavens, and Ki, the goddess of earth.
The name Anunnaki is derived from An, the Sumerian god of the sky. The name is variously written “a-nuna”, “a-nuna-ke4-ne”, or “a-nun-na”, meaning “princely offspring” or “offspring of An. The Anunnaki were believed to be the offspring of An and his consort, the earth goddess Ki. Samuel Noah Kramer identifies Ki with the Sumerian mother goddess Ninhursag, stating that they were originally the same figure. The oldest of the Anunnaki was Enlil, the god of air and chief god of the Sumerian pantheon. The Sumerians believed that, until Enlil was born, heaven and earth were inseparable. Then, Enlil cleaved heaven and earth in two and carried away the earth while his father An carried away the sky.
For additional reading on the Anunnaki, Gaia has as excellent article.