I'm playing a Life Cleric and I love RP'ing epic incantations in the name of my god. While randomly perusing the books at Wal-Mart, I stumbled across a Christian prayer book entitled Prayers that Rout Demons. According to Amazon, "This book contains powerful warfare prayers and decrees taken from Scripture that will break the powers of darkness and release the blessings and favor of God. This prayer tool includes an introduction to spiritual warfare and biblical principles for praying to overcome demonic influence and oppression."
I'm a Bible believing Christian myself (LDS to be precise), and although that book doesn't mesh theologically with my own preferred flavor of Christianity, I found that the biblical references it cites make a great foundation for epic Cleric invocations. I changed a few names and had a great time.
TL;DR: This book cites epic Bible verses you can use for inspiration.