Ugo Farell is most likely a very skilled falsettist, using his falsetto voice much more skillfully than does the popular singer Prince, for example. There are a number of other falsettists who are currently recording, such as Aris Christofellis, Jörg Waschinski, and Ghio Nannini.
There are also a number of counter-tenors, who sing in a slightly lower range, such as Nicholas Clapton, a professor of music who curated a wonderful exhibit at the Handel House in London on the several castrati who resided there to perform for Handel. Clapton was also featured in a British television documentary on the castrato voice.
There are a few natural castrati who have physical anomalies, such as Kallman Syndrome, which keep their voices from changing at puberty. Jorge Cano and Radu Marian seem to fit this category. Some claim that Paulo Abel do Nascimento fit this category, though others claim that he was a real castrato. It is said that his family refused to allow a physical examination to settle the issue after his early death.
The only acknowledged real castrato singing today is Javier Medina, who lost both testicles to medical malpractice at the age of 12. It was, unfortunately, only when he was much older (and completely without HRT), that he realized that he had a future in music. He did not have the intensive voice training that was part of the life of Italian castrati, though his vocal range is, of course, that of a proper castrato.
Javier is a kind and gentle soul. He has been an active and very helpful member of the Castrati History group. I have enjoyed a home-made CD of his singing a variety of songs from opera to Mexican pop.
There are some rare individuals with incredible vocal range, encompassing the treble/soprano, such as the Turkish popular singer Cem Adrian. Hes definitely male, with beard and mustache to prove it. The nude photo of him on the cover of his record album Emir shows that he is definitely male. You can see him in performance of one of the songs from the album, Yagmur (
http://www.youtube.com/watch?v=m7jNQJQXc0k), on Youtube.
The castration of males before puberty to preserve their boyish treble voices as they develop adult lung power probably began about 4,000 years ago. It is now thought that the Sumerian gala (praise singers to the gods) were castrati.
The idea of castrati singers probably spread from the city of Lagash in the years following 2100 BCE and the idea can be traced back to this single origin. There were castrati singers in the Imperial court in China, in the royal court in Java, and in the Byzantine choirs. They seem always to have been rare, however.
They do, however, seem to have been part of the culture in Moslem Spain, which was also a source of eunuchs for North Africa and the Middle East. Some Spanish boys were castrated (e.g., Judar Pasha, a blue-eyed Spanish eunuch general who conquered the Kingdom of Songhai for the Moors), but most of those sold on to the Moslem world were Slavic boys who had been castrated in French Verdun. Slavic eunuchs were so common that the Arabic word for Slav is sometimes used as a synonym for eunuch, just as a corruption of Slav became slave in English.
The use of castrati in the Vatican choir and their spread to more popular music in Europe began with a couple of Spanish falsettists in the 16th century, whom many music historians think were probably actually castrati.