I love watching dramas with huge casts.
More girls than boys:
Brown Sugar Macchiato (School comedy)
Ex-Girlfriend Club (Romcom)
Yamada-kun to nananin no Majo (School comedy)
All the below dramas have about equal no. of male/female cast:
Love Shuffle (great jdrama about love and dating - keeps you guessing)
Mei-chan no shitsuji and Cheer Up take place in school