DirecTV just made its iPad app worth downloading: they've added live TV streaming to it. Of course, the catch is that you can only stream live TV to it when you're on your home network, but that's still something.
The app is free, provided you're a DirecTV customer. There are some restrictions. In addition to having to be on your home network, you can only watch live TV. No access to stuff you've recorded to your DVR, unfortunately. But if you want to watch one thing while your spouse wants to watch another, this is a much cheaper solution than a second TV and receiver.