Miro, formerly Democracy Player (the Internet television application developed by the Participatory Culture Foundation), was just released in late beta -- or at least I was able to find it.
I like it ok in that I get free shows like KQED QUEST Science HD Video Podcasts and Democracy Now and that it plays different formats and is open source and multiplatform, but I don't like the lack of control and metadata information. Let's hope that Adobe Media Player will be more like QuickTime Player. There's Miro links and comments at John Dowdell's blog.
Update: deeper coverage is at MasterNewMedia (7/23/07).