Who are your three favorite female singers?

Sarah Brightman
Oleta Adams
K D  Lang

@richopp,
Funny you should mention singers imitating others. That reminded me of Sheryl Crow and how she sometimes used to sing for others who couldn't.

All the best,
Nonoise

Hard for me to believe that no one has mentioned Beth Hart. My top 3 would have to be 
Beth Hart
Chrissie Hynde
Linda Ronstadt 
Also have to mention Aimee Mann and Stevie Nicks. There are too many other great ones to list and all or most have been mentioned. If you haven’t heard Beth Hart definitely check her out. Her styles album to album or even within an album can range a bit so listen to more than one song before deciding. 

Well many of my older favorites have already been mentioned (Annie Haslam - but no Jane Relf?? - Jennifer Warnes, Natalie Merchant, Sarah McLaughlin, Mary Black, Loreena McKennit, Sandy Denney etc.) but some big ones are missing:

• Bonnie Raitt - I mean "Angel from Montgomery", seriously
• Maddy Prior from Steeleye Span
• Karla Bonoff
• Grace Slick
• Joan Baez

But, with the exceptions of Anneke Van Giersbergen, and Amy Lee, all the great symphonic metal singers were ignored like, in no particular order:

• Simone Simons
• Tarja Turunen
• Dianne Van Giersbergen
• Sharon den Adel
• Floor Jansen
  

Really, how can anyone pick just three?

Elliot, thanks for the Sophie Milman link. 
Just love her voice.