I've been using YUI for the past few months and it's impressive. Not quite as out-of-the-box as you'd hope but the capabilities are endless. Also, I think it's

I've been using YUI for the past few months and it's impressive. Not quite as out-of-the-box as you'd hope but the capabilities are endless. Also, I think it's time we stop mentioning Scriptaculous/Prototype in the same sentence as YUI, jQuery and Dojo.