The technology here changes so much I think I need to pick more than one framework.
Layout
YUI (Yahoo User Interface) - con, very complex.
Special Effects
Lightbox
Confluence uses this one - http://fancybox.net/
Modified with long captions - http://labs.abeautifulsite.net/projects/js/jquery/fancyBoxCaptions/demo/
Comparison and refinement chart - http://planetozh.com/projects/lightbox-clones/