There is one key rule that every artist should recognize. There is no such thing as a good color only good color relationships. So when I'm out and about and I see something that catches my eyes I try to memorize the colors because they demand my attention. Eventually, I have this big beautiful collection of color palettes to call upon for use in later projects.
Places to look for color relationships:
1. Nature: Nature can have some of the most beautiful relationships, but be aware that its not only the plants color that is beautiful, but what surrounds the plant as well.
2.Everyday Objects: This is a little more difficult. Not everything that was created by man has beautiful/appropriate color relationships. I would take examples from things you found striking. Something that caught you attention for an extended period of time.
3. Palettes Online: There are many websites that have palettes available for use for any user. Kuler.adobe.com is a website I would recommend because of the flexibility of the search engine. You get to see what the world imagines when they picture words like "macaroni" or "jealousy". These types of applications help a graphic designer get in touch with people and how they relate color to their reality.