Simply the best
Maybe it is not the best, but anyway it is a very good site rich and full of javascript, CGI and other DHTML code.

Dynamic Drive.com
Tons of Javascripts. You will certainly find your happiness there!

Codebrain.com
Lots of Java programs free of charge to animate your pages.

Freewarejava.com
Plenty of Java programs, tutorials, documentations, links... Lots of good stuff !

Irt Org
A knowledge base and a very instructive FAQ. You will certainly find the answers to your questions there.

Webreference
As indicated in its name...