Windows Media Center
The media program that comes with a Windows PC can interface with the Xbox 360 to stream videos and music to the TV. All it requires is an Internet connection and that the user download necessary software (depending on their version of Windows) for free from the Xbox 360 Media Download Center.
PlayOn
PlayOn allows users to stream content from streaming video websites like Amazon, Hulu, Netflix and YouTube. This program is of especial interest to users with multiple hardware, as PlayOn is compatible with the Xbox 360, PlayStation 3, Nintendo Wii, iPhone and even other media devices like DVRs and TVs.
Connect360
For users with the Mac OS X operating system, the Connect360 program by Nullriver Software allows users to stream their music from iTunes as well as their videos and photos from an Apple computer to an Xbox.