definitely check out
jigoku (aka "hell") (1960).
there's no way i could call this one "j-horror," as that would lump it in with totally different types of films. this one is a pretty horrifying look into, well, hell. it might start off a little slow, but by the end that will be immaterial, as the finale packs quite a punch. you can really see the influence on modern japanese horror films too.
and it just so happens to be on
netflix.
http://criterion.com/asp/release.asp?id=352 for more info.