The Color Scheme Generator is a great online tool that helps you create color sets for graphic design projects. Just select a color from the wheel or enter an RGB value to start, and the generator gives you a set of 4 or more (depending on the settings) colors that work well together, including the web hexadecimal values.
Other options include reducing a palette to "web safe" colors, viewing white and black text on the selected colors, and making slight adjustments to each color in the palette to view new sets and comparisons. Once a palette is generated, switch from the default version to corresponding pastel, dark pastel, light pastel, contrast or pale sets. Once satisfied with the color set, keep the URL for sharing and reference.