recently i've been doing machine t-bar rows (medium wide grip overhand) with an extra stretch on the eccentric and these mofos hit my back really hard
Amazing what a little extra ROM can do, never felt my back work like this before with any other exercise, especially my middle back.
Regarding grips, I've found that wider grip hits my middle back whereas close grip hits the lats more. Another interesting exercise is the horizontal shrug. You set up like in a seated cable row, but instead of rowing to your chest you just shrug your shoulder blades back.