I’ve been using Color Schemer for several years. It’s a simple tool that allows you to find complementary and harmonious colors for your web site. I didn’t have the bookmark on this computer and did a search for it. Openmodo has a great collection of online color palette tools. When you need to choose a color, let these tools help you out.
Before you let an anonymous color generator determine your web site’s look and feel, you should take some time to learn about color theory. The authoritative book on the subject is The Elements of Color by Johannes Itten, of the Bauhaus School. While this book is small and fairly expensive, the knowledge you’ll gain will make it a worthwhile investment. You could also find it at your local library.