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Yes, Chris Pirillo does this everyday! 24/7, it's great. He uses ustream.tv which is free, and seems to be pretty reliable.
 
Just a few:

Ustream.tv (already mentioned)
live.Yahoo.com (this can't handle quite a lot of traffic, though)
Justin.TV
 
You can use various web casting tools such as WebEx, gomeetnow, gotomeeting, on premise RHUB appliances in order to do a live webcast over internet.
 
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