Ignoring this /r/, since it's a topic of importance, I think.
There isn't a single good website for finding streamed or .flv hentai. Hentaitube and a few others did exist, but they've all gone and died (hardly had any good content on them anyway). Aside from the occasional vid on spankwire/redtube/youporn, there's nothing.
But hentai videos? You can download them anywhere, and torrents, etc. are abundant. It'd be nice to have a reliable site with stuff uploaded, so I don't have to commit to a torrent or megaupload download, hoping that what I'm getting isn't shit.