http://colorschemedesigner.com/

It is often difficult for inexperience designers to find colour combinations that work well. Color Scheme Designer helps designers out, by using a variety of methods to suggest suitable palettes. It is extremely easy to use, free and requires no installation. Interestingly, it provides a way to simulate different types of colour blindness, and so can be used to create accessible websites, as well as it education students in some of the principles of inclusion.