I can't believe there's been this many responses and no one has mentioned XBMC. I would take a look at XBMC. (xbmc.org). XBMC, is an opensource software that runs on devices ranging from Windows/Mac to a Raspberry Pi ($40). XBMC has hundreds of addons including many of those mentioned above (justintv, channelone, ustvnow, etc.)

I run XBMC on a Windows 7 box for our main media center client. I also have a (virtual) server that runs Next PVR, which is a free PVR (Personal Video Recorder) software. It's connected to a UHF antenna and is set to record all the shows I watch on Broadcast TV. It also converts the antenna signal into ethernet, so I can watch it in any of the rooms that run XBMC.

We're still using directv (until football season ends) and then we are cutting the cord. Looking forward to that.