Funnily enough I happen to know a singer whose name is Carme (Carmen in Catalan) Cuesta. We went to the same High School, and now she's a quite known jazz singer in Barcelona. Not the same girl though, you can check the "other" Carmen Cuesta at her Myspace site
Not that their voices sound alike, but you might enjoy her anyway.
There's another Spanish singer named Anna Luna who has a wonderful voice and singing. You may like to pay a visit to her Myspace. Listen to "Mediterraneo", I specially love her singing on that one.
The only one that pops into my head right now is Kevyn Lettau. BTW, Carmen has released four CD's. The only one available through Amazon and the like, I believe, is One Kiss. She's released three more on an European (German, I believe) label.
Her "Daydream" CD is one of my all-time favorites, both musically and sonically. It's one of my reference CD's.
Glad to hear someone else loves her voice, and her music.