This is the normal state of a Saiyan. It is characterized by having black hair and eyes, and being born with a tail.

The only true surviving Saiyans where Goku, Vegeta, Napa, and Radditz.

Gohan (Goku's first son), Trunks (Vegeta's first son), Goten (Goku's second son), and Bra (Vegeta's second child and his first daughter) are half Saiyans, which explains why Trunks and Bra do not have black hair and eyes. Gohan and Goten have black hair and eyes because Chi-chi (their mother) also has black hair and eyes. Pan (Gohan's daughter) is one fourth Saiyan, she has black hair and eyes because both of her parents have black hair and eyes.

There are 3 other "surviving Saiyans", but I do not like to use them because they have nothing to do with the REAL story line. They were characters that were made for movies and never really exists. They are Turles, Paragus, and Brolly.


Ohzaru

OHZARU

This is not really a Saiyan level. It's a transformation that occurs when a Saiyan looks at the full moon. A Saiyan in Ohzaru mode multiplies his power 10 times and turns into an enormous waremonkey with a great destructive power. Along the series it is discovered that the transformation is all due to the tail that all Saiyans possess at birth.

When exactly these characters first turned into Ohzaru is not clearly stated, but I do know for sure that Gohan first turns into Ohzaru while he is training with Piccolo for the arrival of the Saiyans.

When Goku and Gohan turn into Ohzaru, they lose all consiousness and lose control while destroying everything in their path. Vegeta trains in Ohzaru mode in his home planet (Planet Veyita) until he is able to control himself. In the end, these three Saiyans lose their tails.


Super Sayain

SUPER SAIYAN
This level is reached after long and hard training, one in which goes beyond the limits put upon Saiyans. The Saiyan changes drastically in the physical aspects, and their spiritual power (power level) reaches impossible levels. It costs a lot to transform, and while being in this transformation they cannot avoid giving out energy and are in a state of nervousness. The physical appearance changes as well, now the Saiyan appears to have green eyes and blond hair.

Goku reaches this level for the first time in the fight against Freeza, being caused fury caused by the death of his dearest friend Krillin.

Vegeta reaches this level while training for the arrival of the androids.

Future (Mirai) Trunks reaches this level after the death of his mentor Gohan.

Gohan reaches this level in the Time Room, while training with his father before the Cell Game.

Chibi Trunks and Goten reach this level easily as if it was part of their nature.
Super Saiyan Dai Ni DanKai

SUPER SAIYAN DAI NI DANKAI
This is not a new level. It is reached by gathering up all of your energy in the Super Saiyan level until you end up with an excessive amount of power. It is more superior than than the regular Super Saiyan level, but all of the all of the power given off and the state of nervousnism are not controllable.

When Vegeta reaches this level he calls himself "Super Vegeta", this was when he intimidated Cell in his second form.

Vegeta and Future (Mirai) Trunks reach this level in the Time Room.


Super Saiyan Dia San Dankai

SUPER SAIYAN DAI SAN DANKAI
This is simply being in the previous level (Super Saiyan Dai Ni Dankai) and taking it to the limit. It promotes an excessive increase in the muscular mass and power, but speed and velocity are lost.

Vegeta and Goku discover this level in the Time Room, but they also find out about the problem (the loss of velocity and speed) and choose to use another level.

Trunks also discovers the problem, but he finds out to late. He finds out during his fight against Cell before the tournament.
Super Saiyan Level 2

SUPER SAIYAN LEVEL 2
Once a Saiyan has reached this level, the individual increases his power enormously and also changes physically. The power, agility, and speed are all equal with the spiritual force. In the physical aspect, the hair is rises a bit more and gets pushed a bit to the back, the force field around them is also more defined.

Gohan reaches this level during the Cell Game after the death of #16 and after his friends are all attacked by the Cell Jr.s.

Goku reaches this level after the Cell Game, in the "Next Dimension".

Vegeta reaches this level while being under the control of Babidi.

Super Saiyan Level 3

SUPER SAIYAN LEVEL 3
This level breaks all of the norms when it comes to power, but it also comes with an enormous waste of energy. The physical aspect changes by an increase in hair and a larger forehead.

Goku reaches this level after the Cell Game in the "Next Dimension".

Gotenks (the fusion between Goten and Trunks) reaches this level in the Time Room, before the fight against Boo.

OHZARU GOLD
This transformation is much more powerful than the regular Ohzaru. In theory, it occurs when a Saiyan (with a tail) looks at the "full Earth" from the planet Plant. It is distinguished from the regular Ohzaru, apart from the increase in power, in the hair color, that now is gold (it is sometimes refered to as the "Super Saiyan" of Ohzaru mode).

Goku reaches this level on planet Plant, fighting against Vegeta-Baby after Kaio-Shin regrew his (Goku's) tail. And just as before (with the Ohzaru mode) he loses all control under this transformation.

Vegeta Baby reaches this level on planet Plant thanks to the gadget that Bulma makes for him.

Vegeta reaches this level after fighting against Lii Shen Long with the same gadget that Bulma had invented.

SAIYAN LEVEL 4
This level definately takes the Saiyan's power to unreachable limits. This level can only be reached for the first time by transforming into Ohzaru Gold first. After that, turning into level 4 can be done without any problems. The physical appearance changes a lot. Since this level really isn't a "Super Saiyan" level, the hair stays black and grows by width, while the entire body (excluding the chest) is covered with a red fur (the Saiyan in this level gets to keep his tail).

Goku reaches this level on planet Plant, fighting against Vegeta-Baby, thanks to the words of Pan.

Vegeta reaches this level fighting against Lii Shen Long with the help of the same gadget that Bulma built.