The hardware you need to create an iTunes-centric media center
To do this, you need a wireless network for your mobile devices, along with either a wireless or wired network for your computers and Apple TV. I recommend an 802.11n network to get best performance; if you have an older protocol, you might consider getting a new router that supports the new 802.11ac protocol so that you're ready for the faster-than-802.11n computers and mobile devices slated to debut later this year.
You also need a $99 Apple TV (one of the black models), which connects to your stereo or TV via an HDMI cable. Running the January 2013 software update, Apple TV supports Bluetooth keyboards so that you can easily search your libraries and your Internet-based media sources. The current third-generation model supports 1080p streamed video, whereas the identical-looking second-generation model supports just 720p.
The Apple TV also supports an optical audio connection and, through Kanex's $59 ATV Pro adapter, VGA video and mini audio output. The former is useful for connecting to stereos for music streaming; the latter is useful for an older TV set.
Streaming video, music, and photos from computers and iOS devices via AirPlay
iTunes on both Macs and PCs supports Apple's AirPlay protocol for the streaming of music, videos, and photos over your network.
Whether you stream from your iOS device or Mac, note that some apps and websites implement DRM (digital rights management), which prevents the video from being shown via Apple TV; you'll get a black screen with a notification message instead.
Using AirPlay from apps. It's supereasy to stream content from iTunes on your computer: Just click the AirPlay button () to choose the media's playback destination (that is, the Apple TV or AirPlay speaker you want to stream to).
Likewise, iOS apps often have the same AirPlay button to direct the media playback from iPads, iPhones, and iPod Touches. Some websites also display this button in their video players.
Tip: If you or your friends use Android devices, there's the free DoubleTwist Player Android app that can stream music and video via AirPlay via the $5 DoubleTwist AirPlay add-on. Just note that it works erratically.
The other thing you can do is use the free Remote app from Apple to have your iOS devices access content in the iTunes libraries on your computers, so they can listen to music, podcasts, or audiobooks; play iTunes U courses; or watch videos stored on those computers. That turns your iOS device into a portable TV or stereo. (The Remote app also lets an iOS device act as a remote control for the Apple TV, substituting for the remote control that comes with the Apple TV.)
To access the media on your computers' iTunes libraries, you need to set up Home Sharing on the Apple TV (via the Settings button), in your computers' iTunes (by choosing File > Home Sharing), and on your iOS devices (in the Settings app's Videos pane) so that they all have the same account. Doing so ensures the devices see each other.
Tip: Don't make your Home Sharing ID the same as your iTunes account. By keeping it separate, you can share the Home Sharing ID with family and friends who you don't want to be able to make purchases from your iTunes account.