Chest-Supported Row Machine
There are countless variations of this machine, but virtually any of them can be a strength athlete's best friend. It allows you to really smash the entire upper back while giving you a break from more axial loading. Many times this is exactly what you need to get past a plateau.
I like the seated kind rather than the ones where you're lying at a 45-degree angle because the natural tendency on those is to arch very hard once the loading gets heavy, which defeats the whole purpose of choosing the chest-supported version.
If you don't have access to the seated machine, rig up your own with an incline bench and a low cable. The best bar to use in this situation is one with a curve in it so you aren't banging it into the bench and can get your elbows behind you far enough to get a strong contraction in the upper back.
Loading on chest-supported rows is secondary to achieving a strong mind-muscle connection. If you want to really get a smoke show going, do them after your deadlifts. You should feel an immensely strong contraction in the upper back due to the maximal loading and increased neural output that came from the deadlift.
Don't rip the weight on the initiation phase. Pull with a "roll on" rep fashion where you initiate with the upper back in a very deliberate manner and then pull aggressively into the strong peak contraction. Hold that puppy for a second before lowering. Two to three sets of 10-12 reps will do the job. – Paul Carter