I've found this cinematography site. Its a bunch of screenshots from visually impressive movies. Right now there are 22 movies up, most of them academy award winners/nominees. I find it really helps me to look at a still as opposed to a moving image which can sometimes fool your eye with the motion.

In several of the movies you can see how they have done the color grading where the vignettes have been added etc. (Black Hawk Down for instance). Most of the screenshots are HD resolution too.

In any case its really cool to look at famous movies to see how Storaro uses color, how Deakins frames a shot, where Kaminski/Spielberg put the eyeline on their reverses etc.

I think you will find it a very useful site.
I did. I just wanted to share because I was excited when I saw it.