-Face pull with external rotation using dumbbells or a cable machine (standing, lying face up, or face down on an incline bench, lots of variations). This is great for the mid and lower back, when done right (your end position after the concentric phase should be in the classic double-biceps pose). If you can't maintain a good upright posture during this, you can perform it supine on a bench.
-"Y"s and "W"s on bench, floor, stability ball, with cables, etc. Make sure these are done right, or you're hitting the wrong muscles, usually the UTs kick in like crazy instead of the LTs and MTs. Get someone to help you when you first start out. Have them feel the area between your spine and the inferior angle (bottom-most point) of the shoulder blade. As you do these exercises, THOSE muscles should kick in. Also, have them feel your UTs or just observe them. If they are kicking in instead, you're doing it incorrectly. Squeeze your shoulder blades down and in, like you're going to put each shoulder blade in the opposite back pocket. You may have to try it without weights first to get the movement right.
-Pulldowns or pullovers if you think your lats are lacking (pull ups, if you can). For pulldowns/pull ups: Get the full range; meaning you return to a "dead hang" position after each rep and you pull the bar to your chest, to get the best lat and mid back activation. And right before you pull down, you always activate those shoulder blades, "down and in". It becomes second nature after some practice; I definitely felt a difference.
-What's also good are the "lifting" diagonals with the band or a cable machine.
-And if they wing: you can work out those serratus anterior muscles, e.g. push up pluses, those pullovers also hit them, overhead presses, and "pec shrugs" are some.
Like mentioned earlier, compound exercises are great and I love them to death (they're more fun and usually more functional), but if there are weak key muscles, injury may be imminent; this is where isolation-like exercises have their place. I hope that helps some. I tend to rant and be long-winded, so sorry for the longer-than-necessary post. :]
Some of this stuff may be contrary to some of what seasoned bodybuilders on RJ do or believe, but I'm biased, being a part of the PT world.