Nobody showing love for the Scott Pilgrim Game? That soundtrack is incredible.
Reagade and Target Reagade on the Spectrum 128k was and still is awesome!!
Other great sound tracks off the top of my head are:-
Xenon II - Amiga
Canon Fodder - Amiga
Speedball 2 - Amiga
Blood Money Intro - Amiga
Check them out on YouTube.
Most recently I really loved the sound track to Valkyria Chronicles on PS3.
I'm surprised more old Lucasarts hasn't been mentioned. Monkey Island 2 still has a massive soundtrack by today's standards, and was amazingly ambitious for the time, not to mention full of great tunes. The updated Special Edition audio does it great justice, too. A couple of favourites:
That second piece is a great, well developed little theme, and yet is for a location in the game you only need to visit once, and very briefly at that, which should give you some idea of the scope of this soundtrack.
Grim Fandango is another great one from LucasArts. Peter McConnell's soundtrack is one of my favourite, featuring some very authentic jazz sounds mixed with some central and south american influences. It has an excellent range, with the end credits producing one of the loveliest performances I've heard in a game:
While a lot of the soundtrack just seems to be having a lot of FUN. Here's another one which can be heard in a room you don't even have to visit to finish the game:
A lot of people have already mentioned the soundtracks that tend to jump immediately to my mind. Bastion, Megami Tensei, Nier, Bionic Commando Rearmed and whatnot are all great, but probably don't need any more mentioning than they've already gotten in this thread, so I'll provide some alternative stuff. First up is one of the main overworld exploration theme songs for the DS version of Ni no Kuni. While most everybody who knows about the game knows that Studio Ghibli did a lot of the general visual design work as well as, naturally, the anime cutscenes, the studio's veteran composer Joe Hisaishi also pitched in and lent a hand with the game's soundtrack, too. A lot of the soundtrack is, in my opinion, just as good as this song, but this one still stands out because of how they time its introduction in the game such that as soon as you're out running in the world for the first time, you really feel its grandeur.
The next game being represented might attract me a little ire since it's Love Plus and while I do think the actual game itself is thoroughly boring to play because of its uninteresting writing in Japanese and accompanying game structure, I found some of its music to be quite good. It's got a good, relaxed pace going for it that accents the general laissez faire nature of the game. I can't find the actual song I'd prefer to post at this moment, but this one is a fine substitute.
No More Heroes 2 is another game I happen to appreciate more for its soundtrack than its actual gameplay. Not all of the tracks are total winners, but I still find myself listening to Kimmy Howell's theme on occasion as well as the little NES-esque theme that plays after you beat a boss. They both seem to call back to earlier eras in music in different ways, so perhaps that's why I like them.
Oh man there is a lot of great soundtracks. Halo, Shadows of the Damned, Bastion, Super Meat Boy and World of Warcraft are among my favorites.
I could keep listing videos - only so I could listen to them. Now I know what to do the rest of the day.
In Amber Clad is just so awesome. Over the rock. Through the bush. Nothing but Jackal.
As many people have said, Shoji Meguro's work is definitely worth noting as it's been consistently great. Darren Korb's soundtrack for Bastion is AMAZING, as is Danny Baranowski's work on Super Meat Boy. I'm a big fan of Yoko Shimomura's work on Super Mario RPG: Legend of the Seven Stars, which is certainly my favorite soundtrack from the SNES. And when it comes to hard rock stuff, nothing beats the original DOOM theme by Bobby Prince, but I actually really enjoyed Yasuhiro Ichihashi and Tomoaki Hirono's work on CastleVania: Harmony of Despair. And for orchestral themes, nothing tops out TAPPY's (or anyone else's) work on Metal Gear Solid.
Here are some of my favorites; tried to choose ones that other people might not have mentioned. I probably posted too many, but if you enjoy my tastes I'll post more!
The World Ends With You:
Valkyria Chronicles II:
Jet Set Radio Future:
Hm, lets see if I can wrack my brain for any tracks that for whatever reason haven't yet been mentioned.
For as much as I feel Final Fantasy XII doesn't get its due, its soundtrack is probably the least discussed aspect of the whole game, which is criminal. I'm a sucker for a game that constantly re-iterates on its central theme, and here is no exception, various aspects of the musical piece "symphonic suite" can be heard throughout the entire game. It is a great moment when it is finally played in its entirety over the closing credits. Whilst this game felt like the black sheep of the main series, for many reasons, its grand sweeping orchestral movements was not of one them.
I know this isn't to everyone's taste, as of matter of fact I've read several reviews that have used this games soundtrack as a negative. For me personally, Madworld lived (and died) on its style, it certainly makes a great first impression, even if that early optimism unfortunately falls down under the repetitive gameplay. The soundtrack itself emphasizes the quick nature of the game, not least of all because each track itself is fairly short. It manages to straddle various genres, from rock to rap, which feeds into the unique feel and theme of a particular stage. A great riposte to those who like to characterize Japanese games as the sole domain of odd and quirky music.
Dark Souls doesn't really contain much music, which only serves to further the impact whenever it does appear. For me, the most memorable of these moments was the arrival at Gwynevere's chamber. For a game that is usually pre-occupied with its bleak and sombre setting, it is a huge comfort when you step into this area and hear the rhapsodic chorus beginning to break through the silence. This is musical dissonance at its best, playing as a bookend to what is one of the most difficult areas in the entire game.
The No More Heroes games are a weird sort, not even being consistent between each other! The first one I thought of as a an extremely self-aware and meta commentary of gaming culture in general, this was evidenced in its music which was a bizarre (but very good) pastiche of various influences, not least of all games. The original game in my opinion provided a more effective deconstruction of the role of the player, and protagonist than Bioshock (which undercut itself terribly), by effectively making your ultimate goal pointless. I say all this because the second game, although crazy plays it relatively straight in comparison, portraying itself more as a reconstruction of what it had broken down previously. As a huge fan of the first (despite its clear flaws), I found the lack of self-referential humor to be somewhat disappointing. That is until I reached the Margaret boss fight, the song itself serving as an in universe "fuck you" for once again playing hero.
As mentioned these are games which are are somewhat questionably designed, but when all the elements come together, it works wonderfully. The implementation of this particular song being so clever in that it works in multiple ways, justified within the narrative as the song the boss character sings to her victims, and also as a clear nod to the audience. Look up the lyrics if you have the time.
Achieved that awesome alone-vibe and nice haunting ambience. Some of the tracks are incredibly catchy, especially the creepy Maridia tune
Monkey Island 2: LeChuck's Revenge:
Very big and diverse soundtrack for a 1991 DOS game. A major improvement over the first one which had a few bad tunes and not enough in the first place
Curse of Monkey Island:
I LOVE the cool reggae feel in this game. It makes the islands come alive.
Much props to the guy above me who mentioned BOTH of these gems in one post.