While there are many books written about the Work, the Rochester Gurdjieff Center makes most extensive use of the texts listed here.

G.I. Gurdjieff
Beelzebub's Tales to His Grandson
Meetings with Remarkable Men
Life is Real Only Then, With "I Am"
Views from the Real World

P.D. Ouspensky
In Search of the Miraculous
The Fourth Way
 

Jeanne De Salzmann
The Reality of Being: the Fourth Way of Gurdjieff

Other readings to explore:

On Attention by Christopher Fremantle

In Search of the Miraculous, pages on self-observation, by PD Ouspensky

In Search of the Miraculous, on Negative Emotions, by PD Ouspensky