I'm listening to the Narnia soundtrack by Harry Gregson Williams and it's outstanding.The songs follow a simillair theme throughout and make a great blend of epic/relaxing melodies.

Recommended

i'm sure most of these have already been said (i didnt bother reading the thread), im just gonna post my favourite soundtracks though:

Donnie Darko
Requiem for a Dream
Pink Floyd: The Wall (of course)
The Animatrix (particularly Kid's Story)
Princess Mononoke
Metropolis
Rocky Horror Picture Show
Akira
Spirited Away
Howl's Moving Castle
Grave of the Fireflies (not alot of music in this movie, but its still great)
Crash
The Matrix

The soundtrack to Frieda is really good, especially if you like (or want to get into) traditionalist Latin music.

I also liked the Cowboy Beebop soundtrack, it has a lot of range with a bit of jazz, blues, country, etc. all great stuff.