SlingPlayer comes to the iPhone, sans 3G support
For the unitiated, the SlingPlayer is an application that lets you watch live and pre-recorded TV on a computer or mobile device. The catch is that you'll need to have a Slingbox hooked up to your home entertainment system to stream that TV over the internet to your computer or phone. The good news is that while Sling Media had originally indicated that the iPhone version of the SlingPlayer would only work with the latest Slingboxes, it looks like most versions of the Slingbox should work.
What won't work is streaming TV over 3G connections. SlingPlayer for the iPhone will only work when you're connected to a WiFi network.