If you're curious as to what Vocaloids sound like, try these songs out!
Jinsei Reset Button - Gumi
Roku Chounen to Ichiya Monogatari (A Tale of Six Trillion Years and One Night) - IA
Think The Future - Aoki Lapis
ONLINE GAME ADDICTS SPRECHCHOR - Hatsune Miku
Black★Rock Shooter - Hatsune Miku
Megu Megu★Fire Endless Night - Gumi
Cantarella - Kaito & Hatsune Miku
Just Be Friends - Megurine Luka
Deep Sea Girl - Hatsune Miku
I could give you about 30 more songs, but I'm not sure you would want to start out with that many...
OTHER THAN JAPANESE STUFF
(because that's all I've been posting for quite a while.)