This has become one my favorite "bodybuilding" back exercises. It's simply unparalleled when it comes to the focused development of the latissimus dorsi, with a special emphasis on the lower portion of the lats.
Simply stand in front of a seated row machine and grab the bar. Bend forward at the waist, as if you're on a crotch rocket. Keeping that same low position, row to about the bellybutton area. Really stretch the lats at the bottom portion of the movement, using the full range of motion. No half reps!
Like it? Then next time replace the bar with a handle and do it one arm at a time.