The all-time best three answers to this are:

1. Those that focus on your weak points

2. Those you are currently not doing

3. Those you suck at

*NOTE: These are usually all one in the same.

If I had to pick...

Squat

For the squat, I'd say the top accessory movements are going to be some type of close stance squat, be it a low box squat, a front squat, or a safety bar squat or cambered bar squat. Just something that's going to be a closer stance than what you would typically do. It's also going to be lower than what you would typically go unless you already squat ass to grass, which most power lifters don't. You're going to squat the legal depth. For this, I'm talking about taking it down, way down. For me, it would be an 10-12 inch box, is what I would use for this. It's a closer stance and it's going to be really fucking hard. It's also a great accessory for your dead lift, by the way.

This is a low box yoke bar squat version. You can go deeper if you like but a couple inches lower than parallel is good.

The next, for the squat, would be the good morning, but I'm not going to say that's for everybody. I'm going to say it's for about 50% of the people out there. Some people heavy triples on the good morning, going real heavy, are great for them. Some people do great going super heavy on the good mornings and just builds the shit out of their squat. Other people, it really doesn't help them a whole lot unless they keep the weight light and do sets of 3 to 5. Either way, I think the good morning falls in there. It's just the execution of the good morning is definitely going to change, and that's, I think, based upon the torso, how long the torso is. A longer torso usually gets by, gets away with and makes better progress doing things like suspended good mornings and heavier good mornings. Shorter torso gets better results doing the lighter sets of 5 and really pushing back on their heels and driving into their hamstrings for that.

This is a squat-morning version. There are many types of good morning movements. This version worked great from Matt Smith. I got more out of a standard more straight legged version with moderate weight with multiple sets with reps of 3-5. 

Because this one still freaks me out I have to post it. This is one I do not recommend unless you are an advanced lifter with a very strong lower back.

The third for the squat would be ... A lot of these kind of coincide with the dead lift. Glute ham raises for the hamstring, working both origin and insertion, and hanging leg raises because you are stretching the hip flexors. You're in a position to where your hip flexors and abdominals are going to work at the same time, and you're not putting yourself in a position that keeps shortening the hip flexors. A lot of what power lifters do, and a lot of the movements that power lifters do, are tightening the hip flexors to a large degree. You can do stretching for the hip flexors and mobility work for the hip flexors and all that other kind of stuff to help with that. I get that. I also get that most don't ever do it. If you throw in hanging leg raises, that's kind of forcing hip mobility work as well as abdominal work on them for that reason.

That's really it for the squat. After that, you're starting to deal with a whole host of different things that I can't really rank in any way whatsoever. They just fall into this hodgepodge of things that may or may not help. It's really specific on the individual and what their weak points are. Those are things that I think can help every power lifter, no matter who they are, how they prioritize them and put them in their programs. Completely a different thing.

BENCH PRESS

For the bench press, some type of close grip bench press would be up there for sure. That includes close grips on boards, close grips to your chest, close grips on an incline. Anything from a close grip perspective is definitely on there. While I'm not a big fan of overhead pressing at all, I do put it on the list because I have seen it help and I've been told it helps a ton of lifters. Never helped me, but we're not talking about my training program here. We're talking about feedback that I've also received from that. Personally if I was to put it in somebody's program, I'd rather see it done as a one armed dumbbell press instead of a barbell overhead, but that's personal preference.

Next would be a JM press, which, when done properly, is kind of the combination of a close grip bench press and extension. I really want to say extensions in here so bad, but a lot of people will fuck it up. I don't want to say it in there. If you have biceps, then extensions are fucking awesome for your bench press. If you don't have biceps then they're not so awesome because the lever's going to become too long. By that, I mean your forearm will hit your bicep at a certain point which kind of shortens up the range of motion a little bit and then you can roll it back. They call them rolling tricep extensions, which are awesome for your bench.

Lastly Dumbbell Presses

DEADLIFT

For the dead lift, I'm going to say deficit dead lifts. I'm not a big fan of rack pulls at all, but I do like pulling off blocks. Basically we're going to say it's exactly the same thing as a rack pull. The bar's in the same position, but instead of pulling off pins, you have a plate sitting on blocks. The difference is how the weight's going to move. How the weight is distributed between a rack and off of the blocks. When you're pulling off of the blocks and you pull onto the bar, that bar's going to flex all the way out to the plates. When you're pulling off pins, that bar's going to flex until it actually gets to the pins. Then, it's going to come up. If you're doing multiple reps, the pins beat the shit out of your back. When you're doing multiple reps when it's off the blocks, it's still going to beat the shit out of your back, but nowhere near the same as what the jarring's going to be when it's off the pins. The pulling off of the blocks still allows a little bit of the bar flex, even if it is a stiff bar, then you're going to get pulling off of the pins as well, which is a more natural type of motion.

Then I would probably put in for the dead lift, the reverse hyper. I don't really think so much for the strength aspect, but from the back health aspect, which is debated. It's debated to death, so I'm basing this off what I have seen.

These would be the top accessories that I feel would be the most effective for Powerlifting.