Some of my favorite mental images of Oia are of the most amazing and very rare "Double-Whammy", the almost simultaneous Sunset and Full Moonrise.
For those who are interested it will happen in about 2 weeks on August 17 between 8:15 and 8:40 PM. If you're fortunate enough to be on Santorini then, go to Oia and grab a spot where you can clearly see westward towards the sunset as well as eastward back towards Fira. The rooftop terrace of the Pelekanos Cafe is the best spot for this event. You can also see it from the Oia Castle overlook, where everyone goes to watch the sunset, above the steps leading down to Amoudi. After the sunset just turn around and look towards Fira. Don't miss it if you're there!