My favourite always changes, but at the moment, my favourite opening is 'sky's the limit' from Persona 4 The Animation, and my favourite OSTs are anything by Yuki Kajiura and the Black Rock Shooter OST~
ichimannen to nisennen mae kara aishiteruuu~ Hassennen sugita koro kara motto koishikunatta Ichioku to nisennen ato mo aishiteruuu~ Kimi wo shitta sono hi kara boku no jigoku ni ongaku wa taenai
Chrono Cross OST Final Boss Battle vs Dragon God AKA Time Devourer ('Final', because the real final battle had no music and that sucked a lot) Song: Dragon God Artist: Yasunori Mitsuda
Kimi wo Shiranai Monogatari ~ Bakemonogatari ED 1 Yakusoku no Paradigm ~ Makise Kurisu Theme (Steins;Gate) Aoi Shiori ~ Ano Hana OP My Dearest ~Guilty Crown OP1 Battle for Everyone's Souls ~ Persona 3 OST Innocence ~ Katawa Shoujo OST Answer ~ G-Senjou no Maou OST ~~~~~~~~~~ I have more favs; those are but a few