Lord of the Rings has the best soundtracks I have ever heard from a movie, and not just the main theme.
My own personal favorite, is the The Ride of The Rohirrim, along with the scene. I prefer to watch the scene, myself.

There is also something to be said about the soundtrack from the movie "Limitless", Happy Pills. Again, hearing it in the movie was better, but what can you do.

Also, Superman.

 

Yeah, I should probably mention that by Watchmen I meant both soundtrack and score.

As for modern musicals I really like Wicked (it has a really catchy music), but they have yet to make a movie version of it.

Limitless has one of these soundtrack where it gets better when you also knows context of scenes where this music was used.

And I can't believe I forgot about Superman. Actually, you can't go wrong with John Williams. This guy can make an epic music even from news theme (legendary The Mission).

 

My favorite OST's along with my favorite song from the OST's:

Samurai Champloo OST - "Msytline"
Avatar the Last Airbender OST - Listen to "Safe Return"
Kingdom Hearts OST - "Hikari Reprice"
Gintama OST 3 - "Night King Hosen"
Full Metal Alchemist OST 1 - "Memories"

 

The Fifth Element
Empire Strikes Back - the darker themes for this middle piece are worth a listen
If you liked Gladiator, get yourself some Dead Can Dance.

Actual musicals:
Les Miserables- I prefer the London stage recording but they're both excellent.
Sweeny Todd
Moulin Rouge

Cheating, since it's just the source material:
Amadeus
Immortal Beloved
also, find a copy of Carl Orff's Carmina Burana- 'O, Fortuna' was used in so many sword and horse epics in the 90's it's ridiculous.

 

Yeah, Hans Zimmer is by far my favorite composer (Gladiator, Nolan's Batman films, Inception), but he's got a couple of, I guess, apprentice types who also do really awesome stuff. I think John Powell is one; he did the Bourne movies. Uhm... Michael Giacchino is fantastic as well; his stuff includes the Incredibles, the Kung Fu Panda movies (freaking awesome), Star Trek (2009), and Lost (there's some really fantastic stuff in there, but also a lot of filler, heh).

Legend of the Fall is an awesome one (James Horner--actually a lot of stuff by him is great). Then you've got some good game soundtracks as well; a particular favorite of mine is the Shadow of the Colossus one.

Let's see... the Pirates of the Caribbean soundtracks are good. Anything by John Williams (like people have mentioned, Star Wars, Superman, Harry Potter, etc), John Howard (lotr)... Uhm, jeez... The guy who scores Miyazaki films, Joe Hisaishi, is awesome; particularly Princess Mononoke and Howl's Moving Castle.

I know I'm forgetting people.

 

I just remembered the Kill Bill (1&2) soundtracks are fantastic.

 

I have a fondness for the soundtracks to Footloose and Top Gun, since most of my childhood took place in the eighties.

The Twister soundtrack actually holds some nostalgic value for me, as well. There was a second album with the score on it, but it was nowhere to be found, by the time I knew it had existed.

I'll also recommend Princess Mononoke. When my niece and nephew were little, they came into my room while I was listening to it, then sat in my lap and listened to the entire thing, while I described what had happened during each scene of the movie. I couldn't believe they sat and listened to the whole thing.

I was also surprised that the feeling ever returned to my legs.

I, too, like the Moulin Rouge soundtrack.

Secret Garden is an old favorite.

I still need to order a copy of The Last Unicorn (Das letzte Einhorn) soundtrack, since you can't get it in the US.

Wicked does have a large number of good songs.

The Ghost In The Shell: Stand Alone Complex 2 soundtrack is great.

The Eureka Seven soundtrack has quite a number of good tracks, depending on your taste.

A lot of the Neon Genesis Evangelion stuff is very good, but there are a million different CDs.

Vince Guaraldi - A Charlie Brown Christmas [40th Anniversary] and, though not AS highly recommended, Vince Guaraldi Trio - Charlie Brown's Holiday Hits.

Hokey though the movie may be, the soundtrack to The Craft had some cool music on it. Like Twister, there was a companion CD with the score, but I never got my hands on it.

It's not a movie, and I mentioned this in another thread, but you can get the soundtrack to Portal 2, FREE from the official Portal 2 website. And it is really good. I can't believe they're giving it away - mind-bogglingly generous.

The Bioshock, and Bioshock 2 scores and soundtracks are also quite good.

I vaguely remember the soundtrack to The Ninth Gate being ominous and rather cool, but it's been a while since I've seen the movie and, unfortunately, by the time I thought to buy the CD, it was no longer available in the US.

 

The song "War" on James Horner's Avatar OST is good. Really energetic.

The soundtrack for the Battlestar Galactica series is good, (but it's Bear McCreary, he's a genius) It's a bit weird with some songs in Gaelic and other languages but that made it more fun imo. Please note that this is a TV show soundtrack, so there are probably a ton of tracks- character themes and such- that are short and not that good as self-contained songs. But each album has some great solo tracks. If you like this, you may like some of the vocal tracks.. Lords of Kobol is also another good vocal track, with Passacaglia and the Shape of Things to come being good "classical" music very different from what I linked.

I second (third,fifth, eighth?) the recs for Inception and Gladiator. If you want,there's a second Gladiator disc titled Gladiator: More Music from the Motion Picture, with more songs, some of which throws in dialogue from the film.

For games, I liked the Halo OSTs. All of them are good but I think the ODST OST is the best it's lower key at times and I like the jazz influenced tracks. But it never does get as frenetic as the others so be warned. As for Reach: Avoid it.

 

So I'm glad Silens brought up Reefer Madness: The Musical, Mary Sunshine (or whatever it's called) is amazing enough, and the whole musical is fucking amazing.

I'd say that most superhero movies have fun scores.

I had something else but I'm drunk enough that I forgot it.

 

On top of listening to the recommendations, I suggest that you consider listening to the Streaming Soundtracks online station.

They've got a vast playlist, and you're bound to hear interesting things that you didn't know existed.

 

The problem with the question of 'best soundtracks' is that you'll usually find, as good or bad as a piece is standalone, it's association with and memories of the film it scored that make it, in some cases vice versa applying too.

You'll likely recognise a few of Ludovico Einaudi's scores. One of my favourite composers at the moment. Specifically the pieces used in This is England in some of the most harrowing and powerful scenes in modern British cinema (those with a stronger stomach might get an impression from this scene). My other favourites of Einaudi's are;

• Nuvole Bianche
• Oltremare
• Primavera (which I'm using in a film this year)
• Dietro Casa
• Ritornare
• Alexandria

Otherwise, some of the classic pieces like Duel of the Fates (despite its similarities to O Fortuna), the Braveheart theme, and the theme to Schindler's List. The Pirates of the Caribbean themes have been fantastic, even if the films weren't. There've been other good suggestions made.

 

Most of the things I'd recommend have already been said, but the score for Hanna was done by The Chemical Brothers, and it's pretty damn awesome. I do have a softspot for the old Buffy the Vampire Slayer soundtrack, but I think that's more nostalgia than anything. I've also been meaning to get the Hollywood version of The Girl With The Dragon Tattoo's soundtrack, as I loved every minute of the music in the film when I saw it, but I can't really comment more without listening to it stand-alone.

I've got the soundtracks from a few animes sitting on my computer, like Serial Experiments: Lain and Noir. The latter has some really lovely violin parts in it, especially the track Canta Per Me. And I have to admit, the opening theme from Lain is probably one of my favourite songs.