I heard this on the Skeptic's Guide to the Universe, podcast #224. Boswell has remixed Carl Sagan and Stephen Hawking (mostly in clips from Sagan's "Cosmos" PBS series), passed them through an AutoTune, and made a pretty neat song and its own music video.
Boswell's The Symphony of Science site has the video in YouTube, MPEG, and MP4 formats and the song itself as an MP3. It's also on Boswell's YouTube channel.
There's a sad undertone, however: Sagan himself is long gone. He should be here to see this.