Oozaru:
When exposed to the light of a full moon, a Saiyan transforms into a giant ape.
While in this form the Saiya-jin's power is greatly increased.
There are two ways to reverse it, one is to chop off the tail and the other is
to get rid of the source of moonlight. Vegeta uses this to battle Goku in the
beginning of the DBZ series.
Super Sayian:
A highly powerful form, Super Saiyan is only released with intense rage. During this
state, the Saiyan's hair will turn bright blond in color, and their eyes will become a
greenish-blue. Half human, half Saiyan's such as Gohan ,Goten and Trunks tend to go SSJ
at a younger age than the pure bloods like Goku and Vegeta.
USSJ:
A sort of mid-level between SSJ and SSJ2, USSJ is a very strong,
yet very slow form. Trunks battle's Cell in this form. Trunks
was more powerful at that time but yet when he tried to hit Cell, Cell got away easily.
This form is useless in my mind.
It takes a long time to attain, and produces a lot of
stress on the muscles causing them to vastly increase in size. It is reached by Trunks.
Only Trunks and Vegeta go into this form.
Super Saiyan 2:
An extremely powerful state, SSJ2 is even more damaging than the ultra-buff USSJ,
without the hit in speed and manuverability. It is characterized by bolts of electricity
that streak around and through whoever reaches this level. Hair becomes longer.