Gohan goes Super Saiyan 2 at the World Tournament
http://www.megavideo.com/?v=APGQCTZ9

Gotenks goes super saiyan 3
http://www.megavideo.com/?v=TNFMKZ7A

Super saiyan 4 gogeta
http://www.megavideo.com/?v=GDV7ZFNX