I've only recently started playing around with ustream.tv. It was very easy to set up and get started. Today, while clearing out my overcrowded aggregator, I came across a reference to Mogulus.com. I immediately set up a new free account, and now I'm playing around with the very cool Mogulus studio.
This site is WAY BEYOND what I was able to do with ustream. You can use multiple cameras, cue up pre-recorded video clips, do storyboarding, have a ticker... very advanced stuff like a real TV station would have in their control room.
You can even embed your TV station like I'm doing here: