Soundtracks, not yet mentioned, that I’d listen to even if they weren’t soundtracks:
Cold Mountain
Dan In Real Life
Moulin Rouge
Velvet Goldmine which is incidentally also my favorite movie
Interesting to see the soundtrack to Heavy Metal listed by other people. I’d never seen the movie but found a soundtrack cassette awhile back, and was surprised by the amount of good stuff on it and how well it worked together There’s not a lot of actual heavy metal music on the album (unless you consider people like Donald Fagen, Devo and Stevie Nicks to be heavy metal) and some of the relative unknowns contribute pretty good songs.
Other ones I like and can think of at the moment - O Brother Where Art Thou and Killer Klowns From Outer Space (OK, the only song I know from that one is the title track by The Dickies, but it’s a great song).
Hedwig And The Angry Inch, great soundtrack, mediocre movie.
Give My Regards To Broadstreet, ditto.
The Crow
Hackers
Sweet and Lowdown, for some very nice old-school jazz guitar.
Boogie Nights
Donnie Darko
Goodfellas is pretty solid, too.
I like the soundtrack a lot more than the movie - I’d forgotten about this one.
I love **The Sponge Bob Square **Pants soundtrack. It’s got Wilco! And The Shins! And Motorhead! I defy you to play that on a Seriously No Good Really Bad Day and not feel better.
Yeah, I’ve been caught by my boss whilst singing along with “Under My Rock”. I don’t care! 
Footloose. The movie was ok for a teen in the 80s. Still, the music was good.
Clueless. Put on the soundtrack and you’re right back in the 1990s.
Madonna’s Evita. I’ve listened to this cd over and over. I think it is far better than the original cast recording.
The film was completely forgettable, but the soundtrack to Steal This Movie is great. I like Sheryl Crow and Steve Earle version of Time Has Come Today, Bonnie Raitt’s cover of It’s All over Now, Baby Blue and Joan Osbourne’s My Back Pages as much as the originals. Well, almost.
Pride & Prejudice (2005) - A beautiful, poetic neoclassical score with echoes of Bach, Handel, Purcell and Mahler. I’ve listened to it over and over again.
Star Trek: The Motion Picture and Star Trek: The Wrath of Khan - Great big orchestral scores with some compelling, memorable melodies.
Country - A great Windham Hill score - open, simple acoustic music that will stick with you.
Xanadu - A guilty pleasure, with Olivia Newton John and the Electric Light Orchestra at their cheesy Eighties best.
The Lord of the Rings - Howard Shore at his most masterful. Passing through Moria, the crowning of the King, Enya’s “May It Be” and Annie Lennox’s “Into the West” are particular favorites of mine.
O Brother, Where Are Thou? - One great old gospel or R&B tune after another.
Ray - The movie was good; hearing all of these great old Ray Charles tracks collected in one place is even better.
Star Wars - Still John Williams’s best (although Amistad is also very good).
Dirty Dancing
Which probably shows my age–and probably identifies me as a former teenaged girl.
I have to admit that I didn’t see the movie in the theater–I was just too young to suggest a movie with that suggestive a title to my parents (and we were never much of a movie-going family).
But I sang “Now I’ve had the Time of my Life” with my choir in Junior High, and I didn’t know what the lyrics to verse two were that I was missing out on (for fear of over protective fathers).
And I remember listening to the music of Dirty Dancing repeatedly on other people’s boom boxes (I never owned a copy of the tape myself)–I have a particularly vivid memory of listening to it during a lock-in at the YMCA with my church youth group.
I did eventually see the movie. And it was ok. Well, better than ok, but that memory is more dilute in impact than the original yearning, and of course the music.
Ooh sound tracks
Iron Eagle
Flash Dance
Streets of fire
Flash Gordon
Highlander
Transformers the CGI movie
The Breakfast Club
Top Gun
Probably more , but dont spring to mind at this time.
Declan
I remember the soundtrack of the 1982 Roy Scheider/Meryl Streep thriller Still of the Night being very good, but haven’t been able to find it anywhere since (and IMDb.com has no listing for it).
Cinema Paradiso has a winsome score that nicely follows the protagonist’s life from carefree youth to lovestruck teen to regretful middle age.
The first Pirates of the Caribbean soundtrack is great - it has a fun, sweeping, romantic power to it that fits the movie perfectly (esp. the track “He’s a Pirate”).
Last of the Mohicans, similarly, has an epic power with an underlying pathos that’s just right for the film.
Saturday Night Fever and Grease, of course. Huge at the time, and still selling all these years later.
White Nights had a great soundtrack…
The Crow, both the soundtrack and the score.
That and The Commitments. I saw that movie for the first time last weekend, and it will be the next soundtrack I buy.
Local Hero and Wag The Dog, but then I’m unabashedly a Mark Knopfler fan. Both movies were good, but not as good as the music.
All the Matrix and Blade soundtracks. Basically just a good mix of techno, industrial and electronica whatnot.
These two definitly. I want to add Kate Bush’s The Red Shoes, the Lost Boys and the third Road Warrior movie, Thunderdome that featured Tina Turner acting and singing “We Don’t Need Another Hero”.
Grosse Point Blank – surprisingly peppy for a movie about an assassin.