If you like to see a woman having an orgasm, then /r/O_Faces is the subreddit for you. As the name suggests, it's the place where you'll see GIFs and standard images that capture girls that are in the midst of a red hot orgasm that makes them go 'Oohhhhhhh!'. To be honest, I hadn't heard of this niche before checking this place out, but it's a damn good idea and just goes to show you what those dudes over at Reddit can make sexy to the point of becoming a fetish.
There are very few rules on /r/O_Faces, expect of course that the girls have to be getting off. I'd say that around 80% of the content is in GIF or GIFV format, whereas the other 20% is still shots. Videos aren't allowed to be submitted to the site and submissions are a little spread out, with around two or three coming in on a daily basis.