Deism is a pretty wide open form of belief - many of the Founding Fathers who were deists used more Christian imagery (Washington called it Providence, Adams called it God/Jesus, Jefferson called it God, Franklin as well), or just used religious language to convey their beliefs. It's not as if they ever became institutionalized, so it is less a organized religion and more a philosophical position about the metaphysical construction of the universe. Regardless, it posits a God, but that "higher power" varies depending on which person you are reading.
Still, it's not widely believed anymore. On the other hand, agnosticism assumes that certain knowledge cannot be known (hence, useless to discuss), so it's in a different category as far as I know. Plus, deism definitely errs on the side of religion, with both beliefs and precepts; even the most extreme of deists thought so. Note Paine's "statement of faith" in The Age of Reason: I believe in one God, and no more; and I hope for happiness beyond this life. I believe in the equality of man and I believe that religious duties constitute to doing justice, loving mercy, and endeavoring to make our fellow-creature happy."