There are. However, you might want to thing about using an AJAX framework in addition to, in instead of, an IDE. jQuery, Mootools, and Prototype are all good choices. They make AJAX development go much, much faster. I'm speaking from experience here.
In terms of IDEs, the way to go is Aptana:
http://www.aptana.com/
I used it for a while. While it is very good at what it does, I ultimately went back to using Vim (a text editor). I was just more productive with the software I was used to.