Kuler
http://www.adobe.com/products/kuler/
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.

To begin with it is important to put the term ‘successful’ in to context. If you think your site will be successful when it starts to compete with imdb.com, ebay.com or amazon.co.uk then it could be a few years before you reach that. However, the 3 attributes to achieve the site’s goals remain the same whether you are adobe.com or a blog about drink coasters.