Debug JavaScript in Internet Explorer
1.Microsoft Script Editor for IE
2.Visual Studio .Net
3.Microsoft Script Editor

Firebug for Firefox
http://getfirebug.com/

Safari + Chrome
http://webkit.org/blog/197/web-inspector-redesign/

Dragonfly for Opera
http://dev.opera.com/articles/view/introduction-to-opera-dragonfly/

Javascript Debug Toolkit for Eclipse
http://www.eclipseplugincentral.com/Web_Links-index-req-viewlink-cid-1372.html

JavaScript Debugger for NetBeans
http://www.netbeans.org/kb/docs/web/js-debugger-ug.html