definitely bleach. i'm a big fan of HIGH and MIGHTY COLOR, Orange Range, UVERworld, etc. and then comes FMA i loved all the opening songs for FMA.
Melancholy of Haruhi Suzumiya (how can you NOT love the ending dance song?) and Kimi ga Nozomu Eien. Yeah.
High and Mighty Color = awesome. VERY awesome.
Oh... okay, add Nana to that list. The anime AND the movies have great music that I listen to again and again~ I mean, they're based around music, but still...
Dunno about best music since it varies by genre, but in my opinion Honey and Clover (ハチミツとクローバー) has the best fitting music.
YUKI - ドラマチック (Dramatic) and ふがいないや (Fugainaiya)
Suneohair - ワルツ (Waltz)
Spitz - 春の歌 (Haru no Uta) and スピカ (Spica)
Suga Shikao - 月とナイフ (Tsuki to Naifu) *Coudn't find a good video*
Join the movement today.
Eureka Seven not mentioned yet? I'm rockin out to all the opening and ending themes of that anime right now. Also, FullMetal Alchemist's soundtrack needs mention.
I also love Ghost in the shell's OST, especially Rising, Inner Universe !
And "Cosmic dare" - Cowboy bebop !!!!!!!!!!
I like Bleach songs. And I daresay that Saiyuki songs are good too.