This is very useful site: www.uiresourcecenter.com , you can find there many free articles and White Papers written by industry leaders about user interface design and rich Internet applications (RIAs). It is maybe one of the most important thing in web development - user interfaces, even if you create applications in Seaside, Rails or something incredible fancy, without good UI it will be still rubbish and useless. So go there and make your user interfaces properly