While I’m a huge fan of Eclipse IDE, I recently discovered Aptana. Aptana is build on Eclipse but optimized for use with Ajax libraries and scripting languages like JavaScript, Ruby and PHP. Like they state it themselves. And you know what? It is as they say. For so far I tried it out. It works really smooth and since I’m used to eclipse it doesn’t take 30 minutes to know how everything works.
If you’re a web developer aptana is worth a try.