Just heard a song on the radio, and - in the jangle pop category - nominate Harriet Wheeler of the Sundays (early-mid 90's group) as an amazing female vocalist. Offhand, can't think of any other tha can so effortlessly glide between notes, not to mention her delightful English accent.
You may have heard "Hideous Towns" or "Here's Where the Story Ends" from their debut album (Reading, Writing, and Arithmetic). IMHO - a great album, and well worth checking out. Pity they didn't release more than 3 albums.
Also, I'll add a vote to the two others for Joan Armatrading. It's perfectly mated to her guitar playing - and pretty unique (deep and clear alto). I've only got her greatest hits album - but it looks like her last album (Lovers Speak) got some raves.