These are a few of my favorite vocaloid producers I think you should check out, as well as some of their songs. (Note that I'm using they/them pronouns regardless of whether or not I know the producer's gender)
GHOST: They're pretty popular, so I'm guessing you've heard of them before. Anyway, they have some very interesting songs and a unique style. Check them out.
Songs: The Distortionist, Appetite of a People-Pleaser, Two of a Kind, Amygdala's Rag Doll
Akuno-P: Also known as mothy, Akuno-P created the vocaloid Seven Deadly sins series and the Story of Evil series. They create very good stories, and you really should check them out.
Songs: The Madness of Duke Venomania, Judgement of Corruption, Servant of Evil, Evil Food Eater Conchita
Mcki Robyns-P: My all time favortie producer. They write Danganronpa V3 fan songs, as well as other original songs. GO LOOK AT THEIR WORK. NOW.
Songs: 'Cause I'm a Liar, Submerged, Killing Harmony, No Don't Hit Restart
KIRA: KIRA is another great English producer, with a unique art style and varying meanings in songs. Make sure you look at some of their work, it will be worth it.
Songs: Burn Me Down, Games, The Day I Die, Circles
Creep-P: Creep-P has some slightly disturbing lyrics and songs, butonce you get past that they are an incredible producer. Some of their most notable songs are based off of the Youtube series "Don't Hug Me I'm Scared". Please look at some of their work.
Songs: Exorcism, TV, Don't Touch Me, NOVOCAINE
MASA: MASA does a lot of work with Hatsune Miku and Gumi, which has resulted in a lot of very wonderful duets. They also started "The Story of the Kitsune and the Demon", which I personally love. They really are great, make sure you look at their songs.
Songs: The Fox's Wedding, ERGONOMIC HERO, The Spider and the Kitsune-Like Lion, Soap Lagoon
Circus-P: I cannot stress how wonderful Circus-P is. They do so much wonderful work that... I can't even explain it. Just go look at their work.
Songs: Last of Me, Breathe, Karma, iNSaNiTY
Steampianist: Steampianist is probably best known for "Secrets of Wysteria", a song based off of the true story of the murderer Albert Fish. Besides that, Steampianist also has some very good songs that you should look at.
Songs: Secrets of Wysteria, The Experiment, La Llorona, Vegetables
Oshiire-P: Oshiire-P, aka Neru, is amazing. They mostly use Kagamine RIn and Len, though they have worked with other vocaloids too. Look at some of there work, it's truly great.
Songs: Abstrat Nonsense, Tokyo Teddy Bear, The Lost One's Weepinig, World Domination: How To
Genjitsutouhi-P: Genjitsutouhi-P, more commonly known as wowaka, is a great producer. All of these people are great producers... anyway, wowaka is great. Check out some of their work.
Songs: World's End Dancehall, Rolling Girl, Two-Faced Lovers, Unhappy Refrain
There you have it! My top 10 producers that you should check out (in no particular order)