Want an artist who sounds like some some you like, tell me here and i'll find some for you.
Depending on your electronic music approach, you should definitively check those artists/albums/circles. I made an inital guide.
First, add Nhato, Camellia, USAO, kors k, KAN TAKAHIKO and banvox to anything. They do mostly anything and they will help you have a lead on what compilation should you pick up.
Dubstep/Trap/Skrillexshit/Future Bass: Eventually you will get to Camellia but also there's Taishi, MK, Freezer, Srezcat, Shandy Kubota (USAO), Hommarju (yes, he does bass music), Akira Complex, DJ Noriken, lapix, Nikizawa, Maozon, Casual Killer, KaSa, and Dirty Androids. banvox also does it pretty well.
Good albums are Krazy Psycho Bass (Lilllium Records), newwav (wavforme), BADASS (Diverse System).
Trance: dj TAKA and Sota Fujimori are a must (although they don't release outside of Konami) but also Ryosuke Tachibana, Clean Tears, LVL.4, Nhato, aran, Xceon (also known as Iceon/Starving Trancer), BlackY, JAVELIN, etc.
A trance circle worth checking is cubegrams, also check either Diverse System AD:TRANCE series and also MEGAREX Ultra Hi-Tech 01.
House/EDM: Check Hyper Juice for nice, more occidental approach on House, so does banvox, kors k, etc. Complextro? Check Camellia, USAO, Nhato, Ryu*, MK, Polyphonix, DJ Genki. Check GAT too (Genki, aran, Ryosuke Tachibana)
EDM Extreme is a nice pick for EDM, so it's Irregular Nation from HARDCORE TANO*C
Hard Dance/Tech Dance/Schranz: Shiron is good at Schranz, so is siromaru, REMO-con is a legend of Tech/Hard Dance in Japan, DJ Noriken, MAD CHILD, Ryunosuke Kudo, KaSa, Ayatsugu_Otowa, etc.
Chech JP_HD albums and Madstiff's Neuropolis I and II.
Happy/UK Hardcore: You should begin with Ryu*, kors k, aran, P*Light, REDALiCE, Minamotoya, etc. Other people who do good Happy an UK are nora2r, DJ Laugh (RoughSketch), M-Project if you like Makina, Fracus and Darwin are also good (not japanese but what the hell), XIO, Hommarju, DJ Genki, some of t+pazolite works, Relect, Yooh, BlackYooh, DJ Noriken, etc.
Pick both X-TREME HARD (Terraform i think) and HARDCORE SYNDROME (HARDCORE TANO*C) compos (they're at 8 and 9 respectively), also the Yatsuzaki Hardcore (Notebook Records) and RAVETAISEN (MEGAREX) compilations are awesome
Hardstyle: There's a new current of japanese hardstyle coming with Massive New Krew, USAO, RoughSketch, P*Light, Srezcat, DJ JEA (DJ SHARPNEL) and DJ Myosuke.
I recomend picking up Splash! and Supremacy from Massive CircleZ) and BREAKOUT BLACK and BREAKOUT WHITE (from Massive CircleZ and UOM Records respectively)
Gabber/Mainstream Hardcore/Speedcore/Breakcore: RoughSketch and DJ Myosuke are both the hottest figures of more harder branches of hardcore. Noizenecio and Kobaryo are pretty good too (Srezcat is Kobaryo) and of course, figures as DJ CHUCKY (M-Project), DJ TECHNORCH, DJ SHARPNEL (as Killingscum), t+pazolite, teranoid (kors k), OZIGIRI, AKIRADEATH, C-Show, Freezer, DJ Genki, SOTUI (friend of mine, pretty chill dude), Round Wave Crusher (not japanese but pretty cool), Bokusatsu Shoujo Koubou, GORESHIT, .
Get HARDGATE anthem and all the Japanese Stream Hardcore series from Psycho Filth Recordings. Get RoughSketch "Maddest Circus Show" for some Techstyle and Gabber.
Rave/Drum and Bass/Breakbeats/Hardcore Rave: A MUST here is DJ Shimamura, also Yudaidhun, DJ Noriken as n.o.d.e, DJ SHARPNEL, kors k as Disconation, DJ TECHNORCH, M-Project, Numb n' Dub, aran, etc. OSTER Project is pretty good at it too.
Get Krazy Psycho Bass (a lot of drumstep songs) and also get STB2 Files: Disconation and J-RAVE compilation. Recursive Call from OSTER Project has a lot of pop drum'n bass songs.
Eurobeat/Parapara: Get Sugano, DJ Command, Y&Co, DOMISO, SOUND HOLIC, etc.
Denpa: IOSYS IS the place to go. There's all the big names in there (ARM, D.watt, uno (RoughSketch), and a few more), also DJ SHARPNEL does a lot of it, so does mosaic.wav and ave;new, also Camellia does a lot of Denpa under his Confetto alias and t+pazolite has done it a few times too, Higedriver could be considered denpa too. Vocalists for Denpa? Try Nanahira, Momiji Yamamoto, Prim (Mayumi Morinaga, pretty chill girl).
Albums? Pretty much anything Touhou denpa, Anything Nanahira too (Colory Starry, Meltical Sugar Wave (with full ver. of Bassdrop Freaks from IIDX PENDUAL) and my favorite, LOP STEP RABBITS!)
Jazz/Progressive Jazz/Rock/Other: OSTER Project and sasakure.UK have pretty good stuff without Vocaloid. Kobaryo releases some good downtempo and SOUND HOLIC releases jazz and metal regularly. Yuyoyuppe has some nice metal songs. And why not check Genki-kun band? (Camellia, Genki, JAVELIN from Massive New Krew and Yukacco) They're pretty good.
Missed someone? Throw it here. Want recomendations? Post here.