As a previous poster mentioned, if you get the EyeTV hybrid TV tuner stick and the (included in box) EyeTV software for your Mac, it can send the live TV signal out to your iOS device. You can use the EyeTV iPhone/iPad app to watch on your iOS device.
A few notes:
1) Your Mac must be on and EyeTV open to stream to your iOS device. The remote app can launch EyeTV software on your Mac if the Mac is on but EyeTV app is not open. I just set my laptop to "never sleep" and turn the screen off (brightness all the way down) when I'm not using it.
2) The streaming quality is great if your stream over your local network. Just create a custom EyeTV connection specifying your Mac's IP address and it connects instantly. For example, my Mac is downstairs and sometimes I watch TV upstairs on my iPhone via my local WiFi network. It's a nice portable TV everywhere my WiFi signal reaches around the house (and out in the courtyard).
3) If you are away from home, I think you must have a WiFi connection for the streaming TV to work. The EyeTV uses the same approach that Apple uses for its "Back to My Mac" connection service through MobileMe. IF Back to My Mac works for you, then EyeTV streaming should work. Streaming quality will depend on the speed of the WiFi connection where you are. I don't think this works over 3G. The makers of EyeTV (elgato.com) have some support files detailing supported routers and settings issues to make this all work.
4) A nice bonus is the EyeTV software on the Mac can record television shows on the Mac, and then prepare (export) it into a format for viewing on an iPhone or iPad or AppleTV. A very functional DVR option. You can even schedule the recordings from the iOS app if you forget to do it while sitting at your Mac.
I mainly use this to watch TV anywhere at home, but when I occasionally do this at a coffee shop or laundrymat while waiting for my clothes I get many oohs and aahs...
Enjoy!