If there's a specific religion with which you are unfamiliar, research the basic beliefs of that religion to form the basis of a fascinating research paper. Because religions are complicated and dynamic, it's impossible to outline the entire doctrine of a religion in a single paper. Instead, stick to a limited topic. For example, you might research the ethical mandates of Christianity or the gods of Hinduism.
If you find a particular religion fascinating, explore it through a historical lens. For example, you might research the historical evidence that Jesus existed or address the social trends that led to the rise of Islam. For such a paper, rely primarily on secular and historical sources, though you can use the religion's sacred texts to inform your historical analysis.
If there's a particular religious doctrine with which you agree or disagree, use research to support your argument. You might, for example, discuss the role of abortion or premarital sex in a specific religion, then provide statistical or scientific evidence either supporting or refuting that religion's claims. Because this is a research paper, support your opinions with facts rather than simply asserting an idea.
Religion and social trends are inextricably linked. In the United States, for example, the Judeo-Christian tradition has influenced everything from government to norms for raising children. Select a specific religious ideology -- such as the idea that children are born with original sin -- and track the ways that idea has influenced a specific culture.