Firebug and Firefox for Various Operating Systems
Komodo for Linux, Windows and Mac OS X
The Free Komodo Edit for Mac OS X, Windows and Linux
Komodo Edit is the free edition of the Komodo IDE. Although Komodo Edit is a useful IDE choice, it lacks a few minor features including an integrated debugger. Regardless, using Komodo Edit is highly recommended before deciding to purchase the pricey Komodo. This version still comes intact with intelli-sense and a code editor that migrates smoothly with Firebug and Firefox.
NetBeans for Mac OS X, Solaris, Windows and Linux
Aptana Studio for Windows
JSEclipse Plugin with Eclipse