“4oD comes to the iPad at last — and getting it is a complete no-brainer while it's free.”Free
First the caveats: UK and iPad only; no AirPlay; and you'll need a Wi-Fi connection. Oh, and its selection of shows is more limited than what you'll get on the 4oD website (the American shows aren't included due to rights issues, and the archive isn't there yet). But, hey — let's not get bogged down in the nitty-gritty, because what's there is actually rather good. There's a decent enough range of shows, and you can browse in a variety of ways, including as a chronology of when the programmes aired, and divided by channel.
The interface isn't very iOS-like, but it's easy to use and implements some familiar features, including sideways scrolling. Importantly, the picture quality is good.
At the time of writing, the app was free, though Channel 4 tells us it plans to move to a 'pay once, watch forever' model at some point. Get it while you can!