Ann Wilson - Fantasic voice. In my opinion, the greatest female vocalist of all time. Heart's cover of Unchained Melody is just wow!
Kate Bush - Her voice is just so unique, even when it changed during the 80s. Can go for soft and gentle, to very powerful to just wacky! The screams in The Big Sky are amazing!
Shirley Manson - Love the sound of her voice. Sounds perfect for the rock music of Garbage. She's one of the many vocalists that prove you don't need to have a powerful voice to be a great singer.
Stevie Nicks - I love how girtty her voice sounds, very unique. Although not all her music is rock n' roll, she and her voice definitely are
Siobhan Fahey - Perhaps I'm biased being a massive Shakespears Sister fan, but Siobhan had the best voice out of the three in Bananarama. It's very deep and calming I feel, but she can also experiment with her voice and it also sounds great.
Siouxsie Sioux - I love how frequently she changes pitch, and the timing of it is perfect so it never sounds out of place. Her 'purrs' sound great too in Face To Face from Batman Returns
Sharleen Spiteri - Holy crap, this woman can sing. I love her voice especially in Halo and Black Eyed Boy, but sounds much grittier in Postcard, so I like how she can also experiment with her voice.
Debbie Harry - Apart from being a great singer and just super cool, what I love about Debbie is that whenever there's a Blondie song that's either reggae, rock, punk or new wave, her voice adapts to that particular style of song, giving great variation and always suits that song.
I'm pretty sure I haven't missed out any of my main favourites and if I have, well, bugger.

Other vocalists I like are Juliette Lewis, Grace Slick, Gwen Stefani, Elisabeth Fraser, Belinda Carlisle and Karen O.