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Search Nico Nico Chorus on YouTube, you might found few great music there
(Most of them are from Vocaloid song)

Here's one of my favorite: https://www.youtube.com/watch?v=A4IdhGYV_Po
You might also want to try Project Diva (game) on PSP to get few songs

I tend to avoid a lot of it and dislike the vast majority of it, but there are a few that get through which'll be stuck in my head for weeks. Namely this one. It's the only one I can remember by heart so I guess it's safe to say it's my favourite.

https://www.youtube.com/watch?v=uD6Qzt1vjGM

Edit: I just looked through my osu! song list, apparently this is vocaloid too so this also.

https://www.youtube.com/watch?v=Cu5fcUa17TU

Maretu

Neru

Deco*27 and his own channel

Jin, well, for Jin you will find some songs here

Orangestar

And those are some of the best artists out there.

I mean... https://www.youtube.com/watch?v=O0TtDeDiHcE Lost one's weeping
this one is really catchy https://www.youtube.com/watch?v=nHV46RLVmtI ...kinda...well...lewd tho
also I like this one https://www.youtube.com/watch?v=A0TuC2oe8sg but its slower and idk

https://www.youtube.com/watch?v=oG2I17Zm8kI
It was stuck in my head for weeks after I first heard it

Used to listen to vocaloid all day long, now, not so much. There are many amazing vocaloid songs but I will post those that I can remember. If some other song goes trough my mind I will surely edit this post.

Miki+Kaito - iNSaNiTY
Megurine Luka - Circus Monster ♥
Miki - mErcy
Megurine Lika - Finale II
Gumi - I love
Megurine Luka - Lie ♥

My favorite Vocaloid/UTAU songs:
Kiku Juon - Ievan Polkka
Megurine Luka - Luka Luka Nightfever
Hagane Miku - Diarrhea
SeeU - Alone
Hakaine Maiko - Song of mushrooms
Hakaine Maiko - LivingDead
Nana Haruka - Ponponpon cover
Momo Momone - Nyanyanyanyanyanyanya!
RUBY & Gumi - Butterfly

Hope this helps :3

I just realized the illustrator in the video https://www.youtube.com/watch?v=i0_thpTpNaw is miwasiba, the developer of LiEat/Alicemare

Always a fan of livetune
Tell your world was and still my favorite
Gumi's songs are catchy too, you should check them too if you have time!

View attached image.

View attached image.