Here is a nice tool to use to create a simple colour palette for a website (courtesy of Rob Howard):
Simply enter the details of one colour that you like and the tool will suggest a palette of other complimentary colours to use.
Here is another tip: if you have a photograph or logo as part of your site design you can pick out one of the colours from the image to use as the starting colour.
For example, the palette I use on this site is based on RGB 239/227/181, which is one of the colours in the photo in the header.
Enjoy :-)
Adobe’s ‘kuler’ is good for finding colour themes and integrates with some of Adobe’s products (such as Flash). There’s also a Dashboard widget for it I think.
http://kuler.adobe.com/
I find it better at finding complementary colours that are not necessarily so adjacent in the colour spectrum - but it’s a shame they made it so hard to extract the hex & RGB values.