The Xbox Media Center is soooo sweet. I’ve had mine for about six months now, and I absolutely love it. I use it mainly to stream music from my computer– we never drop CD’s into our stereo any more because we have our entire 9,000+ song library right there on the XBMC and can pick any song we want with a few clicks of the remote control.
Of course it also has a ton of other spiffy features, like showing lyrics for any song, downloading album information from the internet, streaming video and TV shows, playing hundreds of old (think 1980’s) video games, displaying the weather forecast, and on and on. The Xbox itself cost me around $60 on eBay, and all of the software is completely free (with many thanks to Chancellor for letting me borrow a few hacker parts). I imagine you can get something equivalent with the Apple TV or some other media center, but those things cost a few hundred bucks.
It also helps to have a 62-inch TV.