Sledge hammer work is great on the back and the rear deltoids. The farmers walk is great on the back and the upper, lower, middle traps. Upright rows, rows, one arm rows, deadlifts, over the head lifting, alternating rows, DB rows, shrugs, etc.
The back is a contortionist of a muscle, you can train it in hundreds of different ways.
Hiking with weight is great for the back muscle, using some type of log or drift wood to throw on the back and run or hike with that is great for the back. Dragging, pulling, pushing stuff is great for the back.
The back is an awesome muscle to train, if you are really interested read: "Molding A Mighty Back" by George Jowett.
One of the best back development exercises in the world is the bent press, but perform at your own risk as many claim it's a dangerous lift. When done with proper form, controllable weight, It works and the risks can be limited.
Then there's heavy bag work, if you hit the back hard and heavy, and you use the line of power across your shoulders, shit, your back and shoulders should build up to near super-human levels JUST FROM THAT, if done with consistency, and a mass gaining diet.
Look at the back's of boxers, you get like that from hitting the heavy-bag with force. If you aren't getting some FREAKY back muscle like Jack Dempsey from heavy-bag work, chances are you aren't hitting the bag hard enough to bring about muscle-growth.
My own back is very built up with muscle, however when I hit the heavy bag with a good heavy shot, with good technique, you feel the impact of it in your back. (my muscle isn't built up enough to not feel it at all) and due to this every-time I use the heavy-bag, eat well, get good rest, my back is BIGGER, more muscular, even more ripped.
heavy-bag work is perhaps one of the best exercises for back development that there is, the entire back. Esp up and mid back work.