Many:
Clannad After Story (Toki Wo Kizamu Uta)
Blood+ (Aozora No Namida)
Code Geass R1 (Hitomi no Tsubasa)
Dragon Ball GT (Caprichosa eres tú)
Hunter X Hunter (OP2 Taiyou wa Yoru mo Kagayaku / OP3 Pale Ale / Greed Island OP Pray)
Cardcaptor Sakura (Tobira wo Akate)
Rozen Maiden (Seishōujo Ryouiki)
Mahou Shoujo Lyrical Nanoha (Innocent Starter)
Ryuusei no Rockman Tribe (Kizuna Wave)
.
.
.
etc
@Cropzy: That's subjective. Btw, I only listed OPs of Anime I had watched, if not, "The Creator" would be there, and maybe all fripSide's songs xDD