To me, progression is the key to everything. I have a progression for every exercise I program. This is how you continually build success in an athlete or client. Here is a nice progression for the Inverted Row. Every single person that walks in the door at IPT will be doing some version of the Inverted Row.... It's just a great exercise.
Obviously, another progression/variation would be adding a weight vest.
I have become a huge fan of the TRX (what the row is being performed on). We used to only use rings but the TRX is far more versitale and more comfortable than the rings. And the best part is that they adjust so fast. If you travel or do any workouts at home, you need a TRX.