Oooh, as a musician, I love some anime OST's because they're fun and interesting.
Here's a few of my favorites.
"Cruel Angel's Thesis" Neon Genesis Evangelion:
Anyone that's seen Neon Genesis Evangelion knows that it's a very depressing anime, yet the opener is a certified BOP. So happy and upbeat, and fun. It's a perfect opener.
"Tank!" Cowboy Bebop:
My favorite anime of all time, and consequently, has my favorite opening ever, and soundtrack. Love me some big band jazz and blues.
"Pokemon Theme Song" Pokemon Season 1: Indigo League:
It's a classic. We all know it, that chorus is huge and catchy, and I love the late 80's vibe the song gives me.
"Stand Proud" JoJo's Bizarre Adventure: Stardust Crusaders:
The obligatory Jojo reference goes here. However, I love this opener because one, of course heavy metal, it's catchy, and it conveys exactly what this series is all about. It makes a statement musically, and I have to respect that.
"Again" Fullmetal Alchemist: Brotherhood:
YUI is a talented singer and songwriter, and it shows here in this opener. It conveys everything about the series, and it's a catchy song to boot.
"Battlecry" Samurai Champloo:
It's great. Sure, it's rap, which is very unique in anime, but it's a great song.
"Feuerro Pfeil und Bogen" Attack on Titan Season 1:
You just knew this would be on here. The song is bombastic, catchy, and dare I say, epic and thematic.