For a highly talented, well-recorded female voice it is difficult to beat Diana Krall. She is closely mic'd, but the recordings do no discernible processing of her voice (like reverb or over-dubbing). Most pop music recordings do a lot of processing on female voices. Of course, Krall specializes in jazz standards, which aren't appealing to everyone. Another singer in Krall's league is Nora Jones, and some of her recordings are quite pure. These are just a couple of examples, and female jazz singers will be your richest source of great vocal recordings.
If you're more into, say, country music (he says with a gasp) it is quite difficult to find unprocessed voices. Emmylou Harris, as an example, has done some great recordings in her time, like Angel Band and the Trio albums she did with Linda Ronstadt and Dolly Parton. I'm not much into country music, or folk music, but obviously a lot of female singers hang out in that genre. Anything I've heard of recent recordings is all highly processed and horrible sounding on a great system, but I have heard albums from the 70s and 80s that are more virgin. I am a Linda Ronstadt fan, but most of her recordings from the peak of her career are marred by processing. Actually, some of the best recordings of Ronstadt's voice were not her own albums, but when she sang back-up for other singers, like James Taylor and Paul Simon.
I don't think I've heard a pop recording made after 2000 that doesn't have a lot of vocal processing. Are there any? I enjoy some pop recordings, like Sarah McLachlan and Tracy Chapman, but a great system often highlights nefarious work in the mixing studio. I've often wondered what Lady Gaga would sound like in a purist recording with just her and a piano.
One of the best female voices of all time was Karen Carpenter, but personally I have trouble getting past the drippy 70s pop music. Her early stuff was surprisingly well recorded.
I marvel at Barbra Streisand's voice, but I've never been attracted to any of her material. The women in my life say that's because I'm a guy, and Streisand targeted a female audience. That's a frightening thought.
A long time ago I used to admire the voice of a singer named Vonda Shepard. She rose to fame singing pop standards on the old Ally McBeal television series, but she also does more serious stuff.
The pattern here, with the exception of some jazz material, is recordings from the past. Modern electronics just make it too easy to process everything in the digital domain, and most newer recordings IMHO sound terrible.
