With the web publishing plugin for wowza, you can send streams to lots of outside third party services like UStream. Ideally, your running computer would have your source stream, and wowza, as well as your source encoder, and any other tools you have need for. That eliminates all but the exit bandwidth needed for your streaming service. Wowza has a transcoder plugin too - and you can get daily licenses if you want to try it out on a limited basis.
For the video source, like a webcam or something, you can use FFMPeg, VLC, cameras, etc etc to send to wowza. Wowza is like the Flash Media Encoder. I haven't had a need to try other options.