You'll notice most of what I'm posting aside from metal are female voices... that's always been my thing. The problem is most women in metal sing in an operatic style that is VERY hit or miss for me.
Here's an example of the good, though:
Vibeke Stene has a powerful soprano and it worked incredibly well with Veland's screams. And of course there's a choir. This song just fucking rules in general. Unfortunately the band was never the same after Beyond The Veil.