And here is a free playlist featuring Miku Hatsune, Ren and more. Vocaloids are synthetic programs that can sing. Miku Hatsune recently got world fame and her own concerts with high-tech holographic technonology to bring there enchantment to her fans live on stage. And it worked.. Just search on YouTube for original works or cover version of JPop-songs.
Now enough talking. You can listen by yourself. And some of the tracks have even their lyrics in romaji to sing along :).