Being born a full-blooded Saiyan, Goku has a knack (and love) for fighting and has pushed himself to god-like levels over the years. Throughout his training, Goku has picked up some incredible techniques from Master Roshi, King Kai, Whis, and even taught himself some neat tricks.
Everyone is aware of the powerful Kamehameha, transformation into Super Saiyan, and Spirit Bomb techniques, but there are lots more powerful abilities you may have forgotten Goku ever had. Here's a selection of them from Dragon Ball, Dragon Ball Z, and Dragon Ball Super (no Dragon Ball GT here since it is no longer canon).
10 Kaio Ken
Kaio Ken is a technique Goku uses to enhance his strength and other abilities, at the cost of draining his energy. While the move has returned recently, the Kaio Ken technique was forgotten about once Goku transformed to Super Saiyan for the first time. It made a recent return in Dragon Ball Super when Goku combined it with the power of Super Saiyan Blue in his fight with the assassin Hit. The reason Goku gives for ditching the Kaio Ken for so long is that if he used it with his formidable Super Saiyan form, it would surely kill him.
Kaio Ken was a useful tool for Goku after learning it from King Kai for his fight with Nappa and Vegeta. He even used it in his fight with Frieza.
9 Tail Attacks
Obviously, Goku would have a hard time using tail attacks nowadays, since he no longer has one. When he was a kid, though, there were multiple occasions where the Saiyan tail was used to get Goku out of some tricky situations and one-up his opponent.
Between using his tail as a propeller to get back into the ring of the World Martial Arts Tournament and using it to escape from Tien's grasp with the Four Witches Technique, Goku's use of his tail was often the difference between him losing and being able to fight on. Of course, there was that other side to having the tail where he turned into a giant ape and smashed everything when he saw a full moon, but let's focus on the positives here.
8 Feet Kamehameha
Roshi might have created the Kamehameha, but Goku is its true master. In his fight against Piccolo in the World Martial Arts Tournament, Goku was falling towards the ground head first, bound for defeat. That was until he flipped and shot a Kamehameha out of his feet.
The blast sent Goku sky-rocketing back into the air, allowing him to get in an easy double punch on a very surprised Piccolo. All these years later, we have yet to see Goku use his best technique in quite such a creative way as this again.
7 Using His Speed to "Disappear"
During his fight with Krillin in the World Martial Arts Tournament, Goku seemed to disappear to everyone watching. It isn't until Tien lets us know that he is moving so fast we can't see him that we realize what he is doing. Goku rapidly runs around Krillin until he stops and gives Krillin a jump scare so bad that he falls out of the ring. During this sudden appearance, though, Goku sent multiple strikes into Krillin's chest to send him flying.
With the intense powers of Goku's enemies always escalating, it does not make sense for the creators of Dragon Ball to put a focus on Goku's speed, but he is indeed very fast.
6 Super Saiyan 2
A character going Super Saiyan in Dragon Ball is always an iconic event, which makes it so much more perplexing that the second stage of the transformation is forgotten so easily. Maybe it is easily forgotten because the form tends to be associated with Gohan's fight against Cell, but the first and third Super Saiyan stages are always the most iconic.
The first time Goku becomes an Ascended Super Saiyan, he notes that the power of that form will be no match for Majin Buu. This fact pushes him to show Super Saiyan 3 for the first time, and the second level is most forgotten.
5 Dragon Fist
In canon space, the Dragon Fist has only been used by Goku once in Dragon Ball Z: Wrath of the Dragon. When using the Dragon Fist, Goku flies towards the opponent with his fist outward and flies through their stomach. The ensuing blast of energy that courses through the enemy takes the form of a golden dragon, very similar to Shenron.
When Goku used the Dragon Fist on Hirudegarn, it blasted a hole through the chest of the beast. The Dragon Fist has to be considered one of Goku's most powerful techniques and does not leave him wide open to be attacked, as the Spirit Bomb does. It's disappointing that we don't see this move now.
4 Spirit Bomb Super Saiyan
Like the Dragon Fist, this move was only used once in one of the side movies. In Dragon Ball Z: Super Android 13, Goku absorbs the power of his Spirit Bomb to make himself into a walking bomb, essentially. Android 13 had spent the entire fight essentially kicking Goku's butt. He knocks Goku into the water, which leads him to start asking all of Earth for some energy to make the Spirit Bomb.
Once the bomb is ready, Goku goes Super Saiyan and absorbs the entire energy orb. As Android 13 gets closer to try and strike Goku, his fists start disintegrating away. Goku then takes one final strike at him that injects so much energy into the android that he explodes from the inside out. The Spirit Bomb Super Saiyan is another technique that might kill Goku if he did it again.
3 Destructo Disc Hexa Blade
The Destructo Disc is Krillin's own technique. It is a blade-like energy blast that can cut anything and (almost) anyone. As with almost all of Goku's other moves, he has learned how to use Destructo Disc and put a spin on it. Goku's version starts as a single blade, then separates into five different blades.
He uses this to trick Jiren in the Tournament of Power. Jiren knocks away the first four, then throws the final blade back at the rock Goku is standing on. The falling debris is then cut by the first four blades, and Goku sends Jiren falling. The Destructo Disc Hexa Blade made its debut recently in Dragon Ball Super, so maybe it won't be entirely forgotten.
2 Solar Flare
Solar Flare is not so much a powerful technique as it is a useful trick to blind the opponent. The trick originally comes from Tien back in the Dragon Ball days, and others have used it multiple times (Krillin and Cell in particular). Goku has used the attack a couple of times, but not nearly enough.
He used it against Tien in the World Martial Arts Tournament, against Giant Ape Vegeta in their first fight, and in the Tournament of Power against Caulifla. Maybe his recent use of the technique is a hint that he will start using it to set up more unique attacks for himself.
1 Eight-Arm Fist
The Eight-Arm Fist is a technique where Goku moves his hands so fast that it looks like he has eight of them. It allows Goku to attack and defend himself effectively against Tien, using his Four Witches Technique that grows extra arms from his back.
The technique has not been used since the Dragon Ball days, but it would be amusing to see Goku attacking and defeating a god with illusionary arms.