Second Rurouni Kenshin OVA OSTs, the melodies are a bit overused though, but the music fits the scenes in the anime perfectly.
Then the Jin Roh OST, also tied very closely to the anime.
Mononoke OST, has the same characteristics as the previous two.
The OST I have listened to most of all so far is the Twelve Kingdoms one, I like especially the Piano and Kokyu Memories albums.
Then I am a great fan of all the Hisaishi Ghibli sondtracks, no need to enumerate them, I even like the Nausicaas' ones.
SignorRossi.
EDIT: Oh, forgot Macross Plus OST...