Before you begin: Read the updates at the bottom of the page. This post was written for an older version of the YUI library.
I’ve had nothing but good things to say about the Yahoo User Interface tools. It seems to me like the developers continually add all the things from other libraries that I like into one simple to use, well documented, overall good quality library.
The new addition of the rich text editor has left me no less pleased. I can now ditch the other editors I’ve used in the past in favor of one that will be maintained. (I’ve tried two that worked, but were becoming out-dated and didn’t really have support.)