I program with XSLT and ExtendScript (Adobe's version of JavaScript). My
"library" simply consists of code that I have written for clients. When I am
looking for something for reuse, I use a program called Agent Ransack (free)
or FileLocator Pro to search my folder structure for code that I have
already written. For XSLT, I use the *.xsl wildcard and some terms that I
have likely used in what I am looking for. For example, I might search for
"for-each-group" if I am doing grouping. I usually sort the results by date
modified so I can see the latest code first. It's not an official library,
but it suits my purposes.

Rick