I remember an interview with Pascal Gabriel, one of Dido's producers. In it, he revealed that the vocals for her first single used around 40 different comp takes, and that by the time it hit the shops there had been 10 people involved in its production (as producers).
FORTY COMPS!!! Of course, if you see her live, then it's obvious why. The girl can't sing. Anybody can produce a great vocal if tehy comp it that much. I'd sooner have a good performance which went off-pitch occasionally.
If you're looking for singers who don't need tricks, you can't do much better than the incomparable Emmylou Harris. Also, when we saw her in Manchester, she was supported by Patti Griffin who has simply the best live voice I've ever heard. Her records don't come across so well, though.
Also, there's an English folk singer called June Tabor. I've never heard such power live. Truly, truly awesome.
On another tack, Kurt Wagner from Lambchop, despite having a two-note vocal range, sounds awesome live.
I don't think being a good singer is necessarily about an ability to hit the notes, though. There's something more. Look at Michael Jackson - I mean. I think his music's cack, but there's no denying that he's got that "something" about his voice...