For the "original" texts, there are two main books:
The Elder Edda - also refered to as the Poetic Edda, unknown author(s).
The Younger Edda - also referred to as the Prose Edda, by Snorri Sturluson.
Also
The Saga of the Volsungs - the old norse version of Der Ring des Nibelungen.
The first two deal alot with the mythology. The latter is just one of several legends that survive to this day.