Recently, I re-stumbled upon a website that I absolutely love using for choosing or playing around with different color schemes, Color Scheme Designer. Visually stunning, this online tool includes a color wheel where users can intuitively drag around color selectors and a number of scheme types such as "Mono", "Complement", "Tetrad" that automatically show schemes for real-time color selections.
Color Scheme Designer also provides random presets (in case you're lacking inspiration), advanced color customization, and handy hover-over hex codes for any desired colors.
There is even a "vision simulation" to show you how the colors would look from the view of someone with visual impairments! And "scheme previews" to show you how your color scheme would look on a basic table-based layout! Amazing -- definitely a find worth sharing.