Eerie, Ethereal, Moody, Involving Soundtracks

"Finding Forrester" soundtrack fits this bill nicely. Music of Miles Davis, Bill Frissel, and a version of "Over the Rainbow/Wonderful World" by the late "Great Iz" that is just great. Like Eva Cassidy, he was a young (although morbidly obese) singer with a remarkable voice. He was very young when he died but was very popular in Hawaii, where he lived.

Ryuichi Sakamoto's theme for Merry Christmas, Mr. Lawrence (starring David Bowie) is hard to forget.

The Requiem for a Dream soundtrack fits the bill of dark, eerie, and absorbing. Disturbing movie, with a musical score that's just as dark and chilling.

Enjoyed Mark Isham's soundtrack to "The Cooler" immensely (at least while watching the film). Doesn't really fit the bill, except for the "moody" part, but it is some really traditoioal, smoky, bluesy nightclub jazz sound.

I'll second Peter Gabriel's Passion (Last Temptation of Christ), Long Walk Home (Rabbit Proof Fence) and Birdy. All great. Especially the first 2.

Also -

Apollo, Music For Films (Brian Eno)
Dune (Klaus Schulze)
Traffic - (various) (includes a tune from Eno's Apollo)
Twin Peaks (Badlamenti)
Legend, Sorcerer (Tangerine Dream)
Bladerunner (Vangelis)
Insomnia (David Julyan)
Memento (various)
Pi (various)
Braveheart (Horner)