Titus Lucretius Carus
Titus Lucretius Carus was a first century BCE Epicurean philosopher, and author of the poem "De Rerum Natura" (Of The Nature of Things). A translation by W. E. Leonard is available at Project Gutenberg. The Latin text can be found at IntraText. John H. Lienhard has posted a commentary on Lucretius' atomism.
The Dickenson College blog has a reading of the opening of De Rerum Natura.