@Rainbow Dragon:

Native English vocaloids are actually quite good! *-*/ In terms of pronunciation, especially compared to English vocaloids with Japanese accents.

Thanks for the suggestions! Glass Wall is actually one of my fav English vocaloid songs, but I've never heard the other one before. :o

@mootouman:

Ah, I've seen these producers before! :o I'm not terribly into creepy music, but I'll try to give more of their songs a shot.

I actually have never have heard actual native English vocaloid speakers. I mean I've listened to Luka sing in English but I don't know if that counts.
Wish you luck on your project.

Here's an English song by Len. It's called "For the Better" and I listened to it, it is really good.

Glass Wall by Miku Hatsune (Miku sings in English, very well I might add)

Well hope these help you some.