There are places like XHamster and XVideos that allow you to watch unlimited amounts of porn, but their biggest draw backs are that finding good porn within their navigation systems is a bit troubling. It is so difficult to do that it borders on the impossible. The best way to find their videos is to use a free service like HDVideosTube.xxx where they offer HUGE pics of the videos and have the best ones at the top of the page.
Another big advantage to using HD Videos Tube to find long HD porn videos in particular is that they will give you videos across multiple porn tube sites. Their system shows you so many good videos to watch that you end up with a whole new problem. You become overwhelmed with all of the good porn that is available to you.
I guess it is better to have this new problem than it is to work so hard to find good porn on sites that should be spending their profits on a backend system akin to Netflix. Until then there is always HD Videos Tube!