"Eragon (Inheritance Cycle Book One)" by Christopher Paolini

From Paolini.net: 

"Fifteen-year-old Eragon believes that he is merely a poor farm boy—until his destiny as a Dragon Rider is revealed. Gifted with only an ancient sword, a loyal dragon, and sage advice from an old storyteller, Eragon is soon swept into a dangerous tapestry of magic, glory, and power. Now his choices could save—or destroy—the Empire."