P90X - Shoulders & Arms.

Applying the same principles as Chest and Back, you'll superset these muscle groups to exhaustion. As you'll be using smaller muscles, this might prove slightly less of a struggle - but that doesn't mean you won't be fully maxed when this workout is said and done. Just be sure to keep your form during the latter part of the routine, when you'll be tempted to cheat your range of motion. Maintaining good form is critical for proper muscular development and preventing injury, so stay strict and get ripped!