The Bryn Athyn Cathedral has been streaming audio from their services for years. Now they're also offering live video streaming, using USTREAM.
You can find more information about their audio and video streaming options on the Live Services page of the Bryn Athyn Church website.
I haven't actually tried it out during a service but I have taken a look at the archives on Bryn Athyn Cathedral's USTREAM channel and I was impressed by the quality of the video. I was expecting it to be one badly positioned webcam, streaming grainy footage but, it looks like they've got at least 2 cameras that are well positioned to give pleasant shots of the service and the footage isn't too grainy, even in fullscreen mode.
Let me know if you've tried streaming a service live.
Here's a screenshot of Bryn Athyn Cathedral's USTREAM channel: