Heres something Jim wrote a while back, might help you out.
"The choice of assistance lift pales in importance to the proper execution and loading of the key lifts. Too many younger lifters major in the minors, and they're called assistance lifts for a reason. That's the main point I was trying to make. When evaluating whether an assistance lift has a place in your program, it helps to consider that assistance lifts are intended to accomplish a few specific goals: • Prevent strength imbalances. • Build muscle. • Strengthen weak areas. • ASSIST the basic lifts (squat, bench press, overhead press, and deadlift; or whatever lifts you deem important in your training). Let's take a look at the key lifts and what needs to be strong to do them: Squat — abs, low back, hamstrings, quads. Deadlift — same as squat, plus upper back/lats and grip. Bench Press — chest, shoulders, triceps, lats/upper back. Overhead Press — same as bench press, plus low back/abs. So with this in mind, we have to have assistance work that compliments these lifts and provides balance. Here are some of the best assistance exercises for each area of the above: • Abs — sit ups, ab wheel roll-outs, hanging leg raises. • Low Back — good mornings, back raises, reverse hyperextensions. • Quads — lunges, leg presses. • Chest — dips, dumbbell presses, dumbbell flyes. • Triceps — dumbbell presses, dips, triceps extension/pushdowns. • Shoulders — any pressing exercise. • Hamstrings — glute ham raise, good mornings, back raises, leg curls. • Lats/upper back — pull-ups, bent rows, dumbbell rows, shrugs."