Well, besides those already mentioned, some openings I like are:
In'youchuu Shoku ~Ryoushokutou Taimaroku~ OP, by Marie
Koiiro Soramoyou OP, bu Duca
Haruka Kanata OP, by Tsukiko
Furuiro Meikyuu Rondo ~Histoire de Destin~ OP, by tohko
Primal x Hearts 2 OP, by Ceui
Yoake Mae yori Ruri Iro na OP, by Sakakibara Yui
Gift OP, by Fujiya Misato
Boku wa Kimi dake wo Mitsumeru ~I Gaze at Only You~ OP, by Ayane
Wagamama High Spec OP, by Ooshima Haruna
Bokura wa Piacere OP, by Eisou Gakuen Keiongaku-bu starring I.O.
Tsujidou-san no Jun'ai Road OP, by Hashimoto Miyuki
Koiseyo! Imouto Banchou OP, by Duca