Step-Wise Debugging - For logic errors, there’s sometimes no substitute for peppering break points around likely-looking places, and walking through line-by-line, function by function—in Firebug/Venkman/MSE/Visual Studio—all of which support stepwise debugging.

Expressions Testing - Use the console command line to directly test your expressions. This example pulls names out of email contacts:

Firebug Lite - Firebug Lite works in IE and other browsers, and if you’re using the Dojo Toolkit it comes included, with some enhancements like launching in a separate window, and an object inspector. And of course there’s Firebug itself, but you knew that.

Internet Explorer Developer Toolbar - Microsoft’s Internet Explorer Developer Toolbar is certainly an improvement over what it had before. A lot of inspectors and shortcuts to useful features like cache clearing (which now takes two clicks instead four).