What is the best free software for color correcting video?

I have been doing a lot of photography and have gotten used to editing the look (contrast, color curves, vignette, ect.) of the photos very thoroughly with Photoshop. When I go back to edit video in Sony Vegas, I feel that the options for changing the look of the video itself is quite limited. What is the best free software just for editing the look of video?What is the best free software for color correcting video?avid