This seems to be a recurring question, as the different series of Star Trek are obviously not available yet.
According to TrekMovie.com, here are the following Netflix streaming release dates:
The original Star Trek
Star Trek: The Next Generation
Star Trek: Voyager
Star Trek: Enterprise.
Star Trek: Deep Space Nine
Apparently, only the original series and Enterprise will be available in HD, which is too bad, because I'm specifically looking forward to watching The Next Generation. It's a little weird that Deep Space Nine is being released to streaming a little later than the rest, but whatever. It should take a lot of time to watch the rest of the stuff anyway.