A playlist of unlisted YouTube videos of or related to Japanese music:
Unlisted Japanese music videos

The playlist includes:
Anime music e.g. Theishter - Clannad OST, True Tears Haruhi (piano cover)
Jrock e.g. B'z - Juice (English version live)
Japanese jazz e.g. TRI4TH - Rumble Fish (live) (+ several other live performances from these guys.)

... and other genres.