I am quite shocked this has not become a thread here yet. (O-O)
Personally, if there was a desire from a few of my favorites to "Vocaloid" their voices, I want:
Jero (*For Japanese & English...guh..*) (*q*)
clear (Japanese) (TqT)
Jason Kay from Jamiroquai (English... I know, odd choice, but his voice captures my interest)
Take 6...not one, but THIS WHOLE GROUP. (English, of course)
(Probably will have more when I think of them, but those are definitely my top "I need Vocaloids like this!" vocals.) (^-^)
Just as the title says, it could be anyone: your favorite singers, actors, characters, they kid next door... go wild. :-P