Here are a few JavaScript libraries that I have assembled from the internet. Note that the list is not intended to be a top5 or top20 or anything of that nature. If you want a top 10 javacript Framework just Google it. Consider this list as just a quick bookmark.
JQUERYUI
http://jqueryui.com/download
JQUERY
http://jquery.com/
Script.aculo.us
http://script.aculo.us/downloads
Prototypes
http://www.prototypejs.org/
YUI
http://developer.yahoo.com/yui/
EXT
http://extjs.com/products/extcore/
WebFont Loader
http://code.google.com/apis/webfonts/docs/webfont_loader.html
Google Ajax Library
http://code.google.com/apis/ajaxlibs/documentation/index.html#jqueryUI
Chrome Frame
http://code.google.com/chrome/chromeframe/