Like VLC, MPlayerX is open source and plays a large variety of file formats, but unlike VLC it looks like it belongs on a Mac. In fact, it looks and behaves a lot like QuickTime. I especially like that all the chrome fades out when your mouse is off the window, leaving just the video.
There are other features that I didn’t realise I was missing out on. For example, it remembers where you are in a video when you close the app so you don’t have to go searching for your place next time you start it up. Also, if you are watching a series that is logically named, it will automatically start playing the next episode for you. You can turn that off, but it’s a feature I appreciate. So far, my only annoyance has been the limitation that you can only resize the player from the bottom-right corner. Still, at least it respects the media’s aspect ratio — something VLC can’t do any more!