"Sunshine" was a song by Arrested Development that played extra-diegetically at the very beginning of Smith and Jones. It served to introduce Martha Jones and her family. It was notable for being the first hip hop song used as incidental music in Doctor Who history. It was not, however, the first to appear in the show; this honour goes to "Don't Mug Yourself".
It came from the group's Since the Last Time album, which was released in the UK in September 2006. Despite the fact that Arrested Development are an American band, the album wasn't released stateside in the United States until Halloween 2007. That meant that the US premiere of Smith and Jones was in fact the US debut of the song.