For me, Nobuo Uematsu is incredible. Definitely one of the best composers out there. Just about every good Final Fantasy song was composed by him. Some of his best works can be heard in this video:
Yoko Shimomura is great as well. She composed the music for the Kingdom Hearts series.
Kimi wa ne tashika ni ano toki watashi no soba ni ita
Itsudatte itsudatte itsudatte
Sugu yoko de waratteita
Nakushitemo torimodosu kimi wo
I will never leave you