If you have never used Kuler I highly recommend you check it out. It has been invaluable to me in putting together color schemes. Once there you can peruse the thousands of color themes put together by others or create your own.
Creating your own color scheme is especially helpful you if have a particular color that you or your client would like to use. Kuler has a lot of features to help you easily get your colors into your designs. There are Kuler panels available directly in CS4 and CS5. You can create a personal Mykuler account to save all your created or favorite themes, or you download the public themes directly into your Abobe software of choice. There are lots of different options and tons of uses for this site.
Kuler is now even cooler with the new Community Pulse feature. Pulse is data visualization that displays colors of downloaded Kuler themes on a color wheel. Users can explore the relative popularity of colors by different countries, time periods, and tags. What Community Pulse really shows is how the use of color changes around the globe and at different times of the year. It is like a Google Analytics for Color.
I hope you find this site as helpful as I did. What other tools do you use to come up with color palettes for your designs?