Contreras et al (2010) hooked an EMG up to several strength trained university men to determine which exercise activates which muscle the most. The results confirmed some standard training ideas and brought forth new ones.
Biceps scored the highest mean activation with wide-grip weighted pull-ups, wide parallel-grip weighted pull-ups and ez-bar curls. Latissimus dorsi scored highest, not surprisingly, on weighted pull-ups and rack pulls. The middle trapezius worked best on db bent over rows and elbows out chest-supported rows. The lower traps scored similarly to the middle traps. Upper trapezius was most activated by barbell shrugs, lateral cable raises and military pressing.
Many guys like to work their shoulders to try and get a wider looking frame. The anterior deltoid was most activated by a behind the neck press, a strict overhead press and the incline bench press. The medial deltoid got the most bang out of band face pulls, lateral raises and behind the neck press. The posterior deltoid got it from band face pulls and bent over rear deltoid raises.
The triceps got the highest mean activation from weighted dips, rope extensions and cable extensions. The lower pectoralis portion got it from weighted dips, blast strap pushups and the guillotine press (doing a bench down to the neck), The middle portion of the pectoralis major activated from db bench press, floor pressing and flies. The upper pectoralis got its highest scores on mid-pulley crossovers and banded pushups.
Armed with this information, if one felt they were lacking in any particular muscle, through rep/set manipulation and armed with the right type of exercises, bringing up to par would be much easier.