Instant Color Schemes: This website takes 5 related images from Yahoo Image Search and then show the most prominent 6 colors from each image. Each column of colors is taken from a single image.
Colorhexa.com: This website has all the information you need to create colors. The edit field allows you to enter any color value, i.e., hex number, RGB, or just the plain color word, such as "dark green," and then gives you all the ways to create it. It also lists colors by name, defines all sorts of color terminology, and tells you if the color is web safe. (Huge thank you to Kestrel Verlager for finding and sharing this and the previous resource!)