Javascript

My enthusiasm for javascript waxes and wanes with the tides. Currently, it's been reinvigorated by some of the stuff Google has been doing and the possibilities for lightweight, distributed web applications. An example: the moshi 95 widget

Tools

Yahoo! User Interface
Dojo Tool Kit
JPSpan (sourceforge.net)
Import XML File (quirksmode.org)

Reference

long list of js libraries (edevil.wordpress.com)
top 10 js functions (dustindiaz.com)