This is a tough one, because there are so many contenders that I'm gonna have to make a concerted effort to not write a small novel. I'll try to go with just a few different examples, but we'll see how that goes, heh.
Guess I'll start with my current favorite and wander about from there...
Kevin Penkin - Hanezeve Caradinha
Anyone who recognizes this track from Made in Abyss (making them a fellow anime nerd) knows exactly what I'm talking about. Stylistically, seems to take a lot of inspiration from Hans Zimmer's Now We Are Free from the Gladiator soundtrack (which also deserves a spot on this list), from the lyrics being in a constructed language to the overall feeling you get when listening to it. But while it takes a lot of stylistic cues from Zimmer, Penkin makes this song his own, including adding a few modern synthesized flourishes instead of a strict orchestral/choral arrangement, and Takeshi Saito's vocals are a perfect match for Penkin's melody. Even taken completely out of the context of the series, the track evokes a sense of mystery, discovery, and wonder, with small hints of tension. The entire soundtrack is amazing, but this particular selection managed to send chills up my spine without ever knowing anything else about the series.
Andrea Bocelli & Hayley Westenra - Vivo Per Lei
Sadly, I can't find a good studio recording of this version, but I like it better than the original duet with Giorgia Todrani. Bocelli's powerful and emotional tenor pairs effortlessly with Westenra's soft, angelic soprano, giving you a stunningly beautiful love song to music itself.
John Williams - Theme From Jurassic Park
A classic that everyone knows. Effortlessly blending an entire range of emotions from fear and tension to awe and grandeur, with small hints of quiet, tender moments. It really doesn't get much better than this.
Joe Hisaishi - ...well, almost anything he's done, really...
Often referred to as "The Japanese John Williams", Hisaishi's long-time collaboration with director Hayao Miyazaki have resulted in some of the most memorable scores in recent memory. It might seem like I'm exaggerating, but I don't believe so. Miyazaki's films are artistic masterpieces in their own right. But when Hisaishi's music is added, the combination becomes the closest thing on Earth to true magic. If you can find a copy and are willing to pay the steep prices on imports, the bluray of the Studio Ghibli 25th anniversary concert is worth every penny. Stunning orchestral performance conducted by Hisaishi himself, who is clearly enjoying every note. Two hours spent feeling almost every emotion in the book.
Marylin Manson - Coma White
Probably a bit unexpected, given the rest of this list. Say what you will about Manson, but he knows what he's doing in the studio. Hauntingly beautiful while still in keeping with Manson's overall style, there's not really any warmth or comfort to speak of. But even so, it all comes together into something even his detractors have had a hard time coming up with criticism for.
Kensuke Ushio - lit(var)
From the end of A Silent Voice, the track name makes no sense (nor do the rest of them, by choice, apparently), but it's a beautiful work nonetheless. The first couple of times I heard it, the mechanical sounds of the old piano seemed out of place...some light buzz from a few strings, the slight crunch and thump from some of the keys... but the more I listen, the more that added complexity compliments the simple melody. By the time the rest of the instruments come in, it's a catharsis that matches the film itself. Almost as quickly as they came in, the other instruments drop out, leaving only the old piano to slowly bring the melody to a close with no fanfare. It bookends a highly emotional film (that starts out with The Who's My Generation) with the musical equivalent of a warm hug, and a promise that everything will be okay.
I could probably list a ton more, but I promised to try to keep this from being a novel, and it's getting dangerously close to becoming one.
