The great thing about Netflix is and others have mentioned is the fact you find stuff on there you would have never thought to watch. I've watched a number of documentaries I would have never thought to watch or even known existed if it wasn't for Netflix. As critically acclaimed Breaking Bad and Mad Men are I probably never would have given them a chance if it wasn't for Netflix. It's well worth the $8.00 a month and I'm as cheap as they get. If you can't swing $8.00 you're most likely broke.
netflix has every star trek series and a few of the movies (insurrection/WOK/some other one). It's how I got into star trek. its also got doctor who (new show and a bunch of different 4 parters from the old one) and a whole lot of other classic sci fi shyt.