Fairy Tail's,
Naruto's,
Oda Nobuna no Yabou's (Yasuharu Takanashi is the one responsible for all of them), I like some of Yuki Kajiura's works but not all of them (
Kara no Kyoukai works were possibly her best, imo), some of Hiroyuki Sawano's works (he was brilliant in
Kill la Kill and Attack on Titan) and
Gintama's OST (all the tracks are amazing!).
But if I had to say which OST I prefer the most right
now it would, hands down, be
Shinsekai Yori's OST. It has tracks that are too beautiful to describe with words. Kage no Deshouka's (Song of Shadows) three versions are all amazing - the versions with and without vocals - all of them! Everytime these songs played in the anime, they did for specific reasons and only came on in moments where muk was about to go down. They managed to send chills down my spine everytime.
Do not go to youtube to listen to these tracks. Suggested videos have heavy spoilers in the titles! Check them out here if you want to.
Kage no Denshouka Dai Ichibu
Kage no Denshouka Dai Nibu
This one, especially, is my favorite.
Quite possibly my single most favorite soundtrack in all of anime.
Kage no Denshouka Dai Sanbu
Then there are those amazing ED songs that it has. EDs may or may not come under "OST" according to different people but I'd include them since they help form the overall package. This series has no opening songs and two ED songs. But both the EDs are just simply gorgeously animated and sung beautifully so that kind of makes up for the lack of any OP.
Wareta Ringo
This is Kana Hanazawa's best song that she's ever sung, imo. And one of the most beautiful ED songs I've ever heard, too.
Yuki ni Saku Hana
And because these songs and soundtracks are all intertwined with my memory of this really unique series that had me at the edge of my seat at all times, I don't really think I'm forgetting about these for a good amount of time. Gonna stay my favorite piece of musical works in anime for a long, long time to come.