samurai champloo

Definitely Digimon. The songs - Butter-Fly, brave heart, Biggest Dreamer, Fire!, Never Give Up - are simply wonderful. The background music for the first four seasons, composed by Takanori Arisawa, is excellent too.

Transformers: Galaxy Force/Cybertron has great music too

Gunslinger Girl
Cowboy Bebop
Evangelion
Gunbuster
Etc....

Definitely Digimon. The songs - Butter-Fly, brave heart, Biggest Dreamer, Fire!, Never Give Up - are simply wonderful. The background music for the first four seasons, composed by Takanori Arisawa, is excellent too.

too bad one of the best (if not the best) theme of the first season was never available as is.
its a rendition of another theme but come on, its awesome on its own.
im talking of course about "magnangemons theme". its not called that but thats the only time it has been heard.

Saint seiya has the best music hands down!
Seiji Yokoyama sensei!

The original Ghost in the Shell movie. That soundtrack kicks my ass everytime!!

Bleach

Violinist of Hameln

Escaflowne.

Add my votes for the Cowboy Bebop and Samurai Champloo crowd.

I'm kinda new to the whole anime scene. I have always collected soundtracks from composers I am interested in even if I never saw the work it was composed for, such as Yuki Kajiura, Yoko Kanno, etc. I decided recently to give the Key adaptations a try. So, after I cleaned up all the flood damage (SO MANY TEARS) I've decided Angel Beats music is freaking FANTASTIC. It's currently my favorite anime soundtrack. ROBOTICS;NOTES is another one I can think of that I REALLY enjoyed, and DATE a LIVE has one of the best opening themes ever. I'm trying to list ones I don't hear about too often but I keep circling back to the ones that I just watched (Clannad, Air, Kanon, Angel Beats, Little Busters) I think I have a problem haha.

Some anime with really good music.. There are a lot more but these are just some examples.

Shigatsu wa Kimi no Uso (https://www.youtube.com/watch?v=1HDv2jC_QHg)
Shiki (https://www.youtube.com/watch?v=dixsFSqdjmU)
Mahou Shoujo Madoka Magica (https://www.youtube.com/watch?v=HcgEHrwdSO4)
Angel Beats (https://www.youtube.com/watch?v=-_kW1V1ya6w)
Steins;gate (https://www.youtube.com/watch?v=5rYI2eG3DuQ)
Zetsuen no Tempest (https://www.youtube.com/watch?v=B-JA6j3QOMk)
Magi: The Labyrinth of Magic (https://www.youtube.com/watch?v=uu94eOQqYP4)
Shingeki no Kyojin (https://www.youtube.com/watch?v=Sy6SZ6FLazE)
Fate series (https://www.youtube.com/watch?v=ZKCCs9DNEJs)
Kill la Kill (https://www.youtube.com/watch?v=FOEll_34XsI)
Tokyo Ghoul (https://www.youtube.com/watch?v=3S1NmtWDVYk)

Uchuu Senkan Yamato Original and 2199
Transformers Galaxy Force

I'm a huge fan of Yoko Kanno, all of her music is amazing!
Especially love the Arjuna and Wolf's Rain OSTs.

Simoun is a somewhat rarely mentioned anime with a stellar soundtrack, it's definitely one of my favourites.
Example: https://www.youtube.com/watch?v=B1Dp4Q4iAB0

This compilation album culled from the many Escaflowne soundtracks: Escaflowne: Lover's Only. This is my favorite. It's lovely.

Nodame Cantibile. All of it is classical music.

Either Macross Plus or Cowboy Bebop, in my opinion.

Neon Genesis Evangelion/Rebuild of Evangelion. I love the music and how it sounds with its vintage/classical sound.

Only Yesterday

For me, "Natsu e no Tobira Original Music Collection ". Is a truly masterpiece. It's from Kentaro Haneda. Here can you hear it: https://www.youtube.com/watch?v=Y4C36Jo6CgY&t=0s

saint seiya

Oh, there's plenty. But when in doubt, any score from Yuki Kajiura and/or Joe Hisashi.

In my opinion, it's Blood+ or Eureka Seven. What do you think?

I like the music from Sailor Moon, Digimon, Pokemon, Azumanga Daioh, Blood-C, Attack on Titan, both Ginga Legend series, Tokyo Mew Mew, Wolf's Rain, Jungle Emperor, Eto Rangers and Ranma 1/2.

Attack on Titan :)

I have a long list and they are not in any particular order:
1. Princess Mononoke: Legend of Ashitaka and Princess Mononoke Theme song
2. Howl's Moving Castle: Merry-go-round of life (Image album version)
3. All of Spirit Away
4. Only Yesterday
5. Hellsing Ultimate: the Warsaw Philharmonic Orchestral ones like Song of Demeter and Gradus Vita, Magnolia, Shintou Shite.
6. Ghost in the Shell: Making of the Cyborg, all the chants, (SAC: Run Rabbit Junk, Get9, Velveteen, Psychedelic soul, Torukia)
7. Okami Piano Arrange
8. Red Garden
9. Mushishi: sore feet song
10. Cowboy Beebop: Green Bird
11. Fairy Tail: Overcoming Sadness, Main theme and all the fighting music
12. Mary and the Witch's Flower
13. Demon Slay Kimetsu no Yaiba (Special)
14. Hanasaku Iroha
15. Brave Story
16. Escaflowne: All of it especially Into Gaea, Dance of Curse II, Black Escaflowne, sora.
17. Iblard Jikan
18. Kokia- Fate and Road to glory
19. Le Chevalier D'Eon
20. Ao no Exorcist
21. Shizuka- main theme
22. From Up the Poppy Hill
23. Sangoku V (a game, not anime)- love love #10, the peach orchard
24. Natsume Yuuchingo, especially the OP and ED
25. Summer Wars
16. Tokyo Magnitude 8

I might miss some anime music here and there.

Basically almost all of Studio Ghibli's soundtracks, especially the ones by Joe Hisaishi, Attack on Titan, Fairy Tail, Full Metal Alchemist, Record of Lodoss War, Angel Sanctuary, Pandora Hearts (by Yuki Kajiura), Giant Robo (by Masamichi Amano)

Anything by Yoko Kanno, specially her masterpiece "The Temple of Escaflowne".