Link log of DHTML toolkits. Most promising seems to be nwidgets/netwindows. Articles about it can be found here and here.

http://koranteng.blogspot.com/2004/07/on-rich-web-applications-alphablox-and.html is interesting read about building advanced web interfaces, http://scottandrew.com/weblog/dhtmllibs has annotated list of dhtml libs, http://www.dithered.com/javascript/index.html has some interesting libs,.