If you've tried out web-based palette generators and been underwhelmed, you might want to take Color Scheme Designer for a spin. It combines the features of many other generators into a unique, easy-to-use palette creator.
On the surface it looks like many other virtual palette generators. Dig around, though, and you'll quickly find features not commonly found in your average colour tool.
You can generate single monochromatic, complimentary, triad, tetrad, analogic and accented analogic colour palettes. You can simulate colour-based vision disorders to see how your design colours will look—they even list the percentage of people suffering from the disorders. A preview function populates a dummy web page with your colour scheme, which is a handy tool for seeing how your selected colours look together off the palette.
While the page-simulator is a really great trick, the best feature of Color Scheme Designer is the ability to export your palette not just as a Photoshop palette—a common limitation of many web-based generators—but as HTML+CSS, XML, TXT and GPL (the palette format for GIMP).
Color Scheme Designer is free and requires no signup.