Here's a list:
en.wikipedia.org
Any movie that has a sex scene that is not one here has simulated sex. And as you might notice, the movies that are on there usually are either very low-budget fare, borderline porn movies or only have body doubles and porn actors (or non-actors) perform the sex. The amount of movies containing well-known actors performing actual sex is very low.
Sometimes there are movies where sex scenes are so realistic that it's rumored it's real, for example people in this thread mentioned Don't Look Now and Blue Is the Warmest Colour as having real sex, which is not true. Though the scenes are very realistic and I can understand why people would think this is the case.
The last movie made by the director of Blue of the Warmest Colour did have a scene of unsimulated cunnilingus and that is actually a great example of why we need intimacy coordinators as the scene was apparently filmed against the wishes of the actress while she was drunk. It's the main reason why the film has only been shown at Cannes and will probably never release (also the movie itself is apparently incredibly shit, even outside the fact that it contains actual sexual assault).