Charlotte Church has had a record contract since she was 12 and was the youngest singer ever to have a number one album. Clips from her most recent album are available for sampling here complete with commentary. I must confess I had never heard of her before yesterday.
You can also take a listen on John Barrowman's site to his most recent CD. While I could do without the Broadway/West End arrangements, JB is quite a respectable singer. He does all the standards and I think it is safe to say he has the best voice of any Doctor Who companion ever. And yes, that list includes Billie Piper.