Yeah, so I've been downloading a few J-rock and J-pop music, but am not really sure on what to download off of from the site next. Generally, though, I prefer "fast" songs since I play racing games, but "slow" songs are fine as well... but I'm not really too willing to dig through all those thousands of videogame/anime/etc. OST's.

well, as for me im into more j-rock than j-pop.
try these Artist.
alice9
Aucifer
Gazette
glay
Tommy Heavenly6
L`Arc~en~Ciel
Luna Sea
you can find some nice upbeat songs from them ^^

Uverworld and Orange Range good stuff just jrock

Dude!

Try Amano Tsukiko!