The really well-made movies have a great sense of color and composition. Period pieces offer terrific historical information as well. I try to capture all that information. Using the VLC player, I can pause DVDs at any time and take a snapshot of the screen. These snapshots are quickly becoming an important part of my reference file.
The snapshot above is from Elizabeth: The Golden Age. Not only is the composition interesting, but the hue and lighting are great. For a future piece, I may be inspired by this image and use it to spot test color and value.
And if you use the mosaic filter on Photoshop to simplify the color, you have the basis for a pretty decent palette. Bonus!