first choice - jquery
second choice - also jquery!
you won't go wrong... just pick a project, demo, plugin or
example and
go for it.
the community is huge and growing, and there are several good
books if
you are so inclined ( I like 'jQuery in Action' )
Michael Evangelista, Evangelista Design
Web : www.mredesign.com Blog : www.miuaiga.com
Developer Newsgroups: news://forums.mredesign.com