I have a lot of favourite female singers: Candice Night (and I think she is extremely beautiful as well), her voice gives me goose-bimps when I hear her sing. I think she is my absolute favourite. Patti DOES have a great voice, but it always also depends on the style of music. I think Patti is "rocky", and Candice doesn't do that kind of music; she's more into the "smooth" stuff, and "medieval".
Other great female singers in my opinion are Tarja Turunen from Nightwish, and the female singer from Edenbridge, I don't know her name at the moment.

And of course, Agnetha from Abba has an outstanding voice as well.