I tend to reflexively dismiss single-source news apps, since they're usually not much more than a repackaged mobile site. CNN's Mobile, with push, VOD and live newscasts, is much, much more—but don't expect to get it for free.
Once you've gotten over the fact that no, CNN somehow didn't already have an iPhone app, consider the feature list: CNN.com's text content is formatted into swipeable panels, organized by category. You can save stories for offline reading, and select subjects to create personalized news feeds from CNN's stories. (In blogland, we call these "tags," but hey!) If you're particularly reportorial, there's also a panel for iReport submissions—3GS users can upload video, and everyone can upload stories and photos.
The newsreading and reporting functions look fine, but he app doesn't really start to shine until it starts to stream: Video is available in both VOD and live flavors, the first of which is organized in a catalog, and the second of which jumps in and out of service at the whim of CNN. Here's the theory: Users sit tight with their text content and old clips of Anderson Cooper interviewing panda cubs, or whatever he does, until NEWS BREAKS: Anderson has been mauled by mother panda. This is huge. You get a push notification that says, "Hey, CNN's live right now," which means that the station's content is streamed over Wi-Fi, 3G or EDGE. And, you watch.
CNN says this'll kick in fairly frequently, mostly to correspond with big news events— you know, the kind of things you might rush to a TV to find out more about. It might not sound like much, but conceptually, cable news streaming over the air to the iPhone is, well, a pretty big deal. Sadly, CNN seems to have realized this, so they aren't giving this one out for free: the app will run two dollars when it goes live later this morning. [CNN]