I'd like to make a ditto on VLC - just to remind people its a great open source media player that seems to keep ahead of the commercial stuff like WMP and WinAMP.

I didn't see any torrent programs recommended so I wanted to mention Azureus.

http://azureus.sourceforge.net/

Azureus 3 is bundled with Vuze unfortunately but there is a way to turn that off and make it look identical to Az2. Its other drawback is that its made with Java so its known to be a resource hog. On the other hand, Java allows it to run everywhere so it should work on any OS. There's a lot of flexibility with the settings too.

If you are looking for any peer to peer web broadcasting Sopcast seems to be the standard:

http://www.sopcast.org/