Hello guys,
it's no perfect solution, but still you don't need a PC or a Mac to stream NAS contents to your Apple TV 3.
The Apple TV 3 requires home sharing which is only available on an iTunes device. A NAS is no iTunes device. However certain NAS, such as Synology offer the ability to create an iTunes Server. This is no "home sharing" but it is the same as when going to "Settings" in iTunes and share your library (which also doesn't enable the Apple TV 3 to play your library).
What you can do now is to connect your iPhone or iPad to the iTunes Server on the NAS and then stream video or music (I use iTunes Match, so I only need it for videos) to your Apple TV 3 with AirPlay. Since I am using my iPhone and iPad to control the Apple TV 3 anyway, it's not really an issue for me. This kind of activity is also very kind on power consumption for the iPad.
What you need for this to work:
iPad or iPhone with the latest Remote App. I have an iPad 3 and iPhone 4S with iOS 6.
Any Synology NAS with DSM 4.1 and iTunes Server.
Apple TV 3.
It doesn't matter whether you use LAN or WLAN with your devices. The iPad/iPhone is WLAN only of course.
If you really want Apple only devices (i.e. no NAS) just buy a Mac mini and attach a 3TB USB 3.0 disk to it and use it as "NAS". The Mac mini is about the same power consumption as an average NAS on idle and at the same time is a real Mac allowing you to use it as a computer. I am just a student and after buying an iPad, iPhone and Apple TV no money was left for the Mac mini 😉 or I would have chosen that solution since I really dislike Windows 8 on my PC.