I agree with woofie, Howl's Moving Castle's OST is beautiful~ The soundtracks for a lot of Miyazaki movies are beautiful actually.

I also love the majority of the Final Fantasy franchises ost's. The majority of my favorites come from a VII spinoff though, the prequel Crisis Core. The Price of Freedom is my all time favorite OST. i also really like suteki da ne and waltz for the moon.

As for anime, I love the character songs that came out of Uta no Prince sama. But the OSTs for Shingeki no Kyojin are absolutely amazing.