Thanks for including me in your list! I feel you’ve covered the essentials very well, but I’d like to expand on scriptaculous by pointing out that one of the major components that you enjoy, especially the AJAX features actually belong to the prototype library, which is bundled with the scriptaculous library. The two of them combined are absolute must-haves for anyone doing any serious “web 2.0″ development. Nice round-up!

I personally found moofx and prototype to be particularly useful (scriptaculous uses prototype to do some of its magic)

http://moofx.mad4milk.net/
http://prototype.conio.net/

I’ve also heard some good thinks about jQuery for general JS stuff…

http://jquery.com/

I’m loving JS at the moment, just make sure everything works without it or the Accessibility Gestapo will come for you!