This combination exercise blast the lats, upper back, arms, and core all at once.
Chin-Up and Hanging Leg Raise
This pairing works nicely because it kills two birds with one stone: you can classify it as either a back exercise or a core exercise, depending on where you want to put it in your program. It also helps keep your chin-ups honest because you can't kip or use excessive momentum.
The goal is to do it with your legs straight, but if that's too tough at first you can start by doing them with your knees bent and progress over time to doing them with your legs straight. Doing them with your knees bent is actually a good way to squeeze out a few extra chin-ups too, as the bent legs can be used to give you some momentum. Just don't use that as a license to start flailing around!
Make It Even Tougher
Placing a medicine ball or a weight between your feet increases the core challenge significantly. If you're doing them with bent knees, you can place the weight between your knees. You can also add a weighted vest if you're looking to make the chin-up portion of the exercise harder.