GUI in AJAX

Tools

FireBug 1.2

Reference

MDC Javascript 1.5 Documentation

QuirksMode (less useful now that there are JS Frameworks, but definitive reference)

Sites

Ajaxian

Comet Daily

Free Text Editors

TextWrangler

NotePad++ (PC)

jEdit, (Java)

Aptana Studio Community Edition (for Eclipse)

Vim, CocoaVim (Mac)

Emacs, Carbon Emacs (Mac)

Excellent Text Editors

Textmate (Mac)

SubEthaEdit (Mac)

E-TextEditor (PC)

Advanced

MozRepl