In both Dragonball Z and Dragonball GT, there were six different Super Saiyan levels reached......

-Super Saiyan-
Reached by - Goku, Gohan, Goten, Vegeta, Trunks, Future Trunks, Brolly, Gogeta, Gotenks and Vegito.

-Ascended Saiyan-
Reached by - Goku, Gohan, Vegeta, Future Trunks and Brolly.

-Super Saiyan 2-
Reached by - Goku, Gohan, Vegeta, Gogeta, Gotenks and Vegito.

-Mystical Saiyan-
Reached by - Gohan.

-Super Saiyan 3-
Reached by - Goku and Gotenks.

-Super Saiyan 4-
Reached by - Goku, Vegeta (cheated) and Gogeta.