The single-arm crossover is a great core exercise that employs a very long lever. For this reason, you don't need as much resistance to elicit high muscle forces.
At first this will primarily be a core exercise, but as your core gets stronger you'll receive an amazing pec workout along with it.
We love the workouts that make you ache, the ones that make you shake your fist at the heavens above. This one involves doing one-rep maxes with 60-second negatives, followed by some nice drop sets.