My favorites Jquery ajax librarys / plug-ins
PrettyGallery
PrettyPhoto
Carousel
http://sorgalla.com/projects/jcarousel/#Examples
NyroModal
http://nyromodal.nyrodev.com/
MegaMenus
http://www.sohtanaka.com/web-design/mega-drop-downs-w-css-jquery/
Coinslider
http://workshop.rs/projects/coin-slider/
Nivoslider
http://nivo.dev7studios.com/
Flowplayer
http://flowplayer.org/
Jquery Tools
http://flowplayer.org/tools/index.html