I got rid of cable completely. I setup a Desktop PC with Windows Vista Home Premium (Vista Ultimate will work too) and use an XBox 360 as a TV receiver. Connect the XBox 360 as a Windows Media Center Extender to the Desktop PC. Purchase a Digital TV Tuner for your computer and install. Windows Media Center which is on the Desktop PC will receive signals to watch and can record shows as a DVR. This will let you get all the over the air digital signals (many in my area are in HD 1080i). The XBox 360 will then play the shows live or recorded from the Desktop PC over a home network. I found it best to get a digital TV tuner with 2 inputs connected to the same antenna so you can record 2 TV shows at the same time or watch one while recording another. Also if you have more than one TV, get another XBox 360 as a receiver and connect it to your network. If you don't want to wire your house with Ethernet cables, set yourself up with Wireless N networking and connect the XBox 360 to a Wireless N Bridge (http://www.newegg.com/Product/Product.aspx?Item=N82E16833164036) through an Ethernet cable to make it wireless.
Additionally if you are a fan of www.hulu.com or use Netflix you could purchase a program called PlayOn for 39.99 from http://www.themediamall.com/playon/ which will stream Hulu, Netflix, CBS, YouTube, CNN, and ESPN web content to your TV. This is done by installing PlayOn on your Desktop PC and using the XBox 360's Upnp client to receive the media.
The whole setup may cost a decent amount up front, but I have been using it for several months now and I am saving around $80 a month on HD cable service and the money saved from canceling cable has paid for the original setup cost.
XBox 360: $200
Desktop PC with Windows: ~$400-$600
Digital TV Tuner: ~$70-170
Network Router (Wireless N): ~$70
Is there any way to get cable HDTV without a satellite and without having to pay a monthly charge to Comcast? I would prefer to pay a one time installation and/or access charge than a monthly rate.