God. The Christian God, specifically. I don't find the inexplicable appearance and subsequent creation of the universe by a deity any less valid than the inexplicable appearance and subsequent creation of the universe by a group-hug of the four primal forces. The fact is that humans will never truly know or be able to fathom the truth, so I choose the more optimistic route of thinking that there is something greater than these mortal coils have to offer.
Realists are just pessimists masquerading as something slightly more optimistic. It's such a resigned style of life and I don't see the appeal.
Other popular choices of belief, in no particular order, include:
Chivalry, optimism, monogamy, equality (not apologetically preferential treatment, as I think that only promotes inequality), the right to life for all people, environmentalism and clean energy, peaceful coexistence, young love, soul mates, prayer.
I have a lot to say on Colon's post, but I know that e-peen on both sides and lack of vocal intonation would lead to a flame war rather than a reasoned discussion, so I shall refrain.
