Here I'm going to talk about the machines that I think are worth using if you have them in your gym based on my own experience with each of them.
1. Leg Press
Every gym has at least one. Some free-weight zealots will tell you that this exercise is "for pussies" and that you should just squat and never do anything else for legs. Of course you should be squatting if you can, but some people have legitimate reasons not to squat and can still leg press. Even for healthy people, the leg press is an awesome quad exercise to use as assistance for the squat or to use on "light" leg days. They're also good for calf presses if your gym doesn't have a calf raise machine.
There's actually 2 variations of the leg press: the standard 45-degree version that's usually plate-loaded, and the seated horizontal leg press, which is usually attached to a weight stack. Both are good- the seated one will bring a little more glute and hamstring into play, and the 45-degree one will use more quad unless you put your feet high and wide on the platform.
With either variation, make sure you're doing a full range of motion. Nothing is more worthless than 5-inch range of motion leg presses.
2. Chest-supported T-bar row
This is an awesome way to row and really "feel" it in your upper back. You can get a good stretch and contraction while not having to worry about stabilizing with your lower back. Additionally, since the bar is set in a free-motion joint, you can use this for Meadows Rows, which I just started doing and are quickly becoming one of my favorite rowing variations.
This thing.
3. Any Hammer Strength Pressing Machine
Hammer strength makes a lot of different equipment. Chances are, you've got at least one of their machines in your gym. I'm talking about the lever-based, plate-loaded machines. Hammer Strength makes some awesome pressing machines. I particularly like the decline press, the shoulder press, and my favorite, the Hammer Strength Incline Press, which helped me put on a good amount of chest size.
These machines allow you to use a lot of weight safely and without a spotter, have an arc of motion that overloads the top portion of the movement (where it would normally get easier), and cause the arms to move in towards each other at the top of the movement, which allows for a strong pec contraction at the top due to a greater emphasis on adduction (one of the functions of the pecs). Additionally, each arm moves individually, which is good for preventing left/right imbalances just like dumbbells are. Finally, they use actual plates, which is infinitely cooler than using a pin-loaded weight stack.
The Hammer Strength Incline Press
4. Hammer Strength Row
No, I'm not being paid by Hammer Strength. The row machines have similar strengths to the pressing machines. Dorian Yates used a Hammer Strength row unilaterally on back day. I particularly like the low row, and the high row variant where you use an underhand grip.
Dorian and Mike Mentzer.
5. Cables
Some say cables aren't really machines. I don't give a shit what you call them, but they're versatile. Pushdowns, pulldowns, cable rows (my favorite), straight-arm pulldowns, etc. It's worth using some cables in your lifting arsenal.
6. Leg Curl
Easy to add in after any squat day to give the hamstrings a little extra work. These are actually hard as hell. The lying leg curl is, in my opinion, the best variation by far since you get the greatest range of motion. I've noticed that if I do these with an explosive concentric I feel them more deeply in the muscle and less so in my hamstring's distal tendons, which is a problem for some people.
7. Pec Deck
I really don't use this for chest very often, but I think it's pretty awesome when you put it on the reverse setting for some rear delt flyes.
WHAT THE FUCK ARE YOU SMILING AT
Most gyms will have some variant of this machine. This is pretty good as far as squat machines go, as it's on a lever and gives you a motion that feels a lot like a real squat, with slightly more sit-back. Because of this, it hammers the hell out of your glutes. You can also use a hell of a lot of weight on this so you'll feel like a badass. Use a full range of motion, and don't bounce out of the bottom.
9. Hack Squat
Yet another squat machine. Where the V-squat shifts emphasis towards the glutes, the hack squat is all about quads. It can help you feel the lower part of your quads which might be difficult with regular squats, particularly if you're a low-bar squatter.
10. Side Lateral Machine
There are a few types of these, and they're a good alternative for people who have trouble using their delts in dumbbell lateral raises or can't do them because of shoulder pain. The version I prefer has the cylindrical pads, and I put my hands outward, rather than on the handles, so it really looks like I'm flapping like a bird. You can get a great pump from a 20-rep set of these.
Like this, except with your hands off the handles and without blatantly inconsistent shadowing.
11. Smith Machine
Say WHAT?
I work out at a Planet Fitness from time to time (hate away, my girlfriend has a membership because it's cheap and convenient and I don't mind it there one bit). Since they took away the benches due to some unfortunate accidents that I wish I had witnessed and because the dumbbells only go up to 60, the only way to get a decent chest workout is on the Smith Machine. It's actually pretty decent for incline and decline benching as well as shoulder pressing to the front and behind the neck. It pretty much sucks for flat benching though. It's a favorite of some "pretty" big dudes like Dorian Yates Jay Cutler. Barbell pressing is still better in my opinion, but if this is your only option you could definitely do worse.
It can also be used for bent over rows, which is a favorite of John Meadows. I wouldn't squat or deadlift on it (I've tried both, very awkward) but front squatting is actually pretty decent on it. I spent some time doing that freshman year of college, when the Cook/Douglass weight room didn't have a squat rack for a while. Once I was able to get back to squatting I was hitting PRs within a few weeks since I had built some extra quad size.
It should be noted that John Meadows does like to deadlift on the Smith Machine (maybe I'll give it a shot again) and Dorian Yates did Smith Machine squats for most of his pro career instead of free squats. Just goes to show that no one thing works for everyone. Either of those could certainly be viable options for someone.
Ahnold Smithin' it up in the 70s.
This isn't necessarily a comprehensive list. If I think of more machines that are good, I'll revisit this in the future.
