OK, so I didn't like the overall consensus that your options on shoulders were front and lateral raises, dumbbell and barbell presses, and flys. So I did some research, cuz, really, would you expect anything else from me?
Admittedly, I didn't find much we didn't already know. Your shoulder is a highly complicated bit of biological machinery designed to allow the arm to move with a huge range of motion. Your deltoids, pectorals, triceps and trapezoids all play a role in this, and this is why isolation/targeted exercises for the deltoids are so few - it's simply too hard to minimize involvement of the other muscle groups that are also attached to the same joint. Not to mention, to hit just one head, or even to hit all three heads, you're looking at one of a handful of specific movements....
Flexion exercises (think frontal raise) and abduction exercises (lateral movement of the arms away from the body) will both hit your anterior and medial heads.
Transverse abduction (i.e. bent over lateral raise) will engage the posterior and lateral heads.
Transverse extension (think pull backwards, elbows out, moving in a horizontal plane at shoulder level) will engage almost solely the posterior heads.
And that's about it. That whole big huge range of motion through your shoulder joint is mostly moved by muscles other than your deltoids - your traps, lats, and pecs. Outside these planes of motion, you start engaging these other groups more than your delts, which is awesome if that's what you want to do, but that's not what we want at all, now, is it?
Your flexion exercises are pretty obvious - front raises and the myriad of variations on them. Dumbbell and barbell, both to shoulder-height and all the way up. Abduction exercises, same damn thing but to the side. You can sub out cables for freeweights for any of these and lose no efficacy, just be mindful of where the cable will run from top to bottom of the rep - you don't want to get tangled in it or otherwise do strange things to its angle. You can combine the two motions with moves like
Cuban presses - start with the shoulders rolled forward, weight at about thigh-height, and left the arms kind of like an upright row. When your elbows are at shoulder height, rotate the arm to bring the weight from below to above the shoulder, and complete the movement like an ordinary dumbbell overhead press. You will hear some folks advocate these
horrid behind-the-head deals - but I don't. The bottom of the rep - behind the head - is a huge stress on your rotator cuff and AC joint. Enough weight for your deltoids to reach failure is enough to be of serious concern of damaging the ligaments, especially once you do actually reach failure. The reverse is also true - light enough to not jeopardize the joint is probably not enough to reach failure in 8-12. Be it shoulder presses, raises, or lat pull downs, extreme caution is advised for exercises that demand weight be held
this way at the top or bottom of the rep - or better still, don't do exercises that call for it at all.
Transverse abduction exercises come in two flavors. The first is face down (be it bent over or actually lying on a bench), start with the arms down straight, elbows pointed out and slightly bent, and move the weight by rotating the arm from straight down to straight out. Cables are going to be somewhat more effective because the angle of the force of resistance does not change relative to the joint's plane of motion. With dumbbells, the force is always straight down from the hand, so there's a massive shift in the angle relative to the joint's plane of motion from bottom to top of the rep. It's the flat bench dumbbell chest fly problem flipped upside down. If staring at the rubberized mat isn't your bag, the other option is to do these upright. Using a cable tower or crossover, start by holding the arm straight out, elbow slightly bent and pointing away from the body, and an overhand grip on a cable handle, and extend the arm outward until it is out straight. Either alternate arms with a cable tower, or you can do both at the same time using a crossover.
Transverse extensions look a lot like rows - what changes is the plane across which you move the weight. You draw the weight toward the body at shoulder-height, like
row to neck,
rear delt row, or
face pull.
Personally (and feel free to disagree), and Mark has
indirectly stated the same, I feel it's very easy to overtrain your anterior and posterior heads because of everything they're involved in. All chest exercises hit the anterior head. A lot of bicep exercises involve the anterior deltoid as well - though frequently unintentionally. Plus you hit the anterior deltoid head-on on your shoulder days, no matter which iteration of THT you're doing via overhead presses and frontal raises (if you're subbing them out based on the
Exercise Bank). Your rear delts, well, they just don't need it. For one, they're little, because biomechanically speaking, they don't do a hell of a lot. Yes, there are eleven billion modifications of ways to hit them. No, you don't need to do a damn one. See the lil footnote there from Mark on the shoulder section of the Exercise Bank? Mark calls out rowing movements, but any kind of downward pull will hit them, too. Truth be told, back day you're hitting your rear delts really,
really frigging hard. Pull downs, pull-overs, rows, the million different types of pull-ups all hit your rear delts to varying degrees. Bent-over lateral raises do engage the lateral head, which makes them somewhat useful for something other than overtraining, and really, you have better options on your traditional lateral raises, and
Mark's variation on cable laterals.
TL;DR - Limited quantity of exercises is caused by limited biomechanical purposes for engaging solely the deltoids. Effective movements tend to be variations on front and lateral raises, and on overhead presses. No clue why folks have gotten so creative with the rear delts, cuz they don't freaking need it, but if you've ever wanted to smack your self in the face with a cable attachment here's your chance.
thought you were looking for novel movement, not just different equipment! No matter, hopefully the novella will be useful info at some point... 
