I'm developing a Plex Media Server client and version 1 is just about ready to go to the Yahoo QA pipeline maybe within another week. CRASHPlayer.
Final QA is in process. We are trying to keep the code base stable and not add new functionality, just bug fixes. It's not the prettiest app you'll ever see in version 1, but is quite full-featured for a first release. We'll work on aesthetics in the next version.