For anyone looking to get some new muscle in their back check out these articles and I applied some anatomy to exercises that work the back so you know what muscles your working.
Bent row (wide grip works back more): Lats, traps, rhomboids, teres minor/major, infraspinatus, posterior deltoid.
Lat pulldowns (front): Teres major, lats. Especially the center part of the lats.
Pullup: Traps (inferior), rhomboids, teres major, lats.
Chinup: lats, teres major, to a lesser extent traps and rhomboids
Cable rows: traps, rhomboids, teres major, erector spinae, posterior deltoid.
barbell shrugs: traps, secondary emphasis on deltoids.
http://www.t-mag.com/nation_articles/235pow.jsp
http://www.testosterone.net/html/body_85back.html