Here's a link to a recording of Alessandro Moreschi - the "last castrato" - who was singing (I believe) right up until the early 20th century.

While listening to it, I was enthralled and I have to say a bit creeped out. Although once revered for its purity, power and range - described as the angel's voice - the castato's voice did not incite in me the same feelings described in so many of the texts I had read. It was foreign to me and I couldn't read it as beautiful. It was strange and I was ill at ease with being unable to decide whether it was 'masculine' or 'feminine' or even childlike. There are voices out there today that I enjoy (although the names don't come instantly to my mind) that fall into the androgynous range; there are popular male singers that are famous for their falsetto... women who sing in the deeper range... Does the trauma involved in the making of the castrato matter? And what did the English, French, German, Italian of the C13th-20th think?

Vernon Lee, a writer that I've recently become very interested in, wrote a story called "A Wicked Voice" which recounts a composer obsessed with trying to resolve his love for the crystalline beauty of the castrato's voice and his knowledge that it is a voice made of pain. Lee, like the composer of the story, was obsessed with the castrato's voice and tried to reconcil herself to the same problem: reconciling the voice of ultimate purity and perfection (heavenly perfection) with manmade construction and an unavoidable defination as unnatural. (The third sex is also being examined here.)

I've written the above from reading several of Lee's stories (and I'm planning on hunting for more in Toronto soon) but I haven't started an indepth study as of yet. Still for those interested in reading I've posted a link. Let me know what you think