Quick First Read
What the Buddha Taught by Walpola Rahula (Recommended)
Good Question, Good Answer by S. Dhammika
Introductions to the Early Texts
In the Buddha's Words by Bhikkhu Bodhi
The Life of the Buddha by Ñāṇamoli Bhikkhu (Recommended)
Buddha-Dhamma for University Students by Buddhadasa Bhikkhu
Comprehensive Introductions to All Traditions
The Foundations of Buddhism by Rupert Gethin
The Buddhist Religion: A Historical Introduction by Richard H. Robinson
An Introduction to Buddhism: Teachings, History and Practices by Peter Harvey