How to stream iTunes content to Apple TV 2G without a Mac or PC?
You can play media that originates on an iOS device using AirPlay to send it to the Apple TV. AirPlay is built in to iOS.

If you have a PC or Mac, you could turn on iTunes Match and send the entire library to the cloud. At that point, you could ditch the PC/Mac and let Apple TV play from the cloud. iTunes Match requires a yearly subscription fee.

Neither of these features requires you to have a Mac or a PC, but neither helps much if all your media is on NAS.