Internet History Sourcebooks Project
Fordham University: Ancient History Sourcebook: Religion in Ancient Rome
This site, from the Internet Ancient History Sourcebook, provides a series of primary source documents on Rome's religious history. It includes prayers and hymns as well as writings from Cato, Cicero, Livy, and Plutarch.
Other
Roman Religion and Burial Practices
Details from the Sussex Archaeological Society about Roman religious practices: Roman gods, what Romans were like, and how the Romans buried their dead.