New vocaloid songs come out every hari so it is a bit much to keep up with, however if anda want new, good vocaloid songs I would recommend creating an account on Nico Nico Douga, they finally released the English version so its much nicer to use
link anda need to create an account to watch videos. I would give anda some video to watch but as anda berkata there are way to many and most of them are good so really I find the best thing to do is to get lost on youtube, just find a vid and just keep clicking on the related vid section after anda watch each one. If anda keep clicking vocaloid vids eventually all of the recommended vids will have Japanese titles because they have all been directly uploaded from nico nico douga, while some of these song are not very well known some of them are still very good. but I can give anda some songs
1, 2 fanclub
Deep-Sea city underground
Remote Controller
complete evil lolita complex
Dragon Rising
Wave
Starlight Keeper
Eternity
Revolution Green is the Enemy
Rise and Fall of Physic Girl
Bonus Stage
Gensouka
ReBIRTH
Ice Sculptures
The serigala that fell in cinta with little red riding hood
permen Physiologist
Soleil
Phantom thieves Peter and Jenny
Well I could go on but then We'd be here all hari so have fun!