Sure to become a favorite!
The Happy Soul Cardigan by Wool Addicts calls for Sunshine, a mercerized organic cotton.
Sizes/#balls:
S-M (37.75 in) / 13 balls
L-XL (42.5 in) / 15 balls
It's knit using sizes US 15 and 17 needles so this knits up quickly.
This pattern is available as a PDF download.