For Anime you could make a partnership with kissanime.com, their the best website for free anime.
Smule is a karaoke website, listening/watching recordings would be cool.
Primewire is an awesome website to watch any series, but you might have problems in the legal department.
Honestly i mostly care about Anime, and it seems to be the most possible one.
Love your website! really cool way to socialize, watching series/movies/anime at the same time with people would be the dream.
From all the other websites ive seen with the same concept this one seems to be the most easily accessible so i hope to stick with it,