Kuler has been the preferred choice of many web designers (including myself) for creating the perfect colour scheme for quite some time now. Kuler contains thousands of user generated colour palettes, which you can use straight away or modify to your needs. New themes can be created from just one or multiple colours, with the added ability to upload an image to Kuler, which analyses and extracts the colours it contains to create a new theme. You can also engage with the Kuler community by rating and reviewing colour schemes.
Colour Lovers is an amazing design resource which is built around a very active community of colour enthusiasts. Amongst the vast collection of schemes available you’ll find a wealth of information on current design trends & patterns. If you’re looking to do more than creating a new palette for your site and want to get involved with a community dedicated to colour and design, then I would certainly recommend taking a look at what Colour Lovers can offer!
Color Scheme Designer
I consider this a “Light” version of Kuler, where you can quickly create colour schemes and export your final palette in various formats, including html/css. This allows you to quickly and efficiently copy & paste the hex values of each colour so you can apply it to your design.
Useful Firefox Addons
An extensive colour picker, advanced eyedropper and palette viewer that allows you to extract and work with colours found on websites with ease.
Find out what CSS rules specify a given color
Eyedropper – get the color of any pixel in the browser window
Color Picker similar to ones found in Photoshop and Paint Shop Pro
Palette Viewer and editor
Webpage Color Analyzer
& Many, many more.
ColorSuckr allows you to right-click any image on the web and extract the 12 most common colors from it. You can then build color schemes from the results.