With most intermediate bodybuilders, back training seems to have taken a back seat to other muscle groups. However, competitive bodybuilders, like Lee Haney, recognize the importance of this muscle group in total body development. Lee's back is his best body part, and he won the Mr.Olympia Contest for several years. In reality, the back muscles respond very well to resistance training. Even so-called "hard-gainers" can develop good back musculature without a tremendous investment in time. However, you do need to make an investment in effort. I've always trained my back muscles very hard, and as a result, the dead-lift was my best lift as a power-lifter.
The back is composed of several muscles. Most bodybuilders just train the lats (latissimus dorsi), but the traps, and the spinal erectors are equally important for balanced development. The smaller back muscles, such as the teres major and minor and the rhomboids, are hard to isolate and thus are seldom targeted directly during back workouts. Some bodybuilders target the upper, middle and lower back, which is an appropriate training approach. In short, just don't train your lats to the exclusion of the other back muscles.
I generally train the traps on my shoulder day following the delt exercises. I normally do upright rows and shrugs. Upright rows develop both the delts and traps and serves as a good bridge between these muscle groups. I normally do 3 sets of 8 reps for both upright rows and shrugs. Note: upright rows can be a problem exercise for people with shoulder problems so proceed cautiously. Additionally, I do abs and back extensions (spinal erectors) after every workout - four times a week.